Adding support for STS Token Exchange Creds in core:

- IETF specification is available here:
https://tools.ietf.org/html/draft-ietf-oauth-token-exchange-16

grpc.def

@@ -111,6 +111,7 @@ EXPORTS
     grpc_google_refresh_token_credentials_create
     grpc_access_token_credentials_create
     grpc_google_iam_credentials_create
+    grpc_sts_credentials_create
     grpc_metadata_credentials_create_from_plugin
     grpc_secure_channel_create
     grpc_server_credentials_release

include/grpc/grpc_security.h

@@ -328,6 +328,31 @@ GRPCAPI grpc_call_credentials* grpc_google_iam_credentials_create(
     const char* authorization_token, const char* authority_selector,
     void* reserved);
 
+/** Options for creating STS Oauth Token Exchange credentials following the IETF
+   draft https://tools.ietf.org/html/draft-ietf-oauth-token-exchange-16.
+   Optional fields may be set to NULL. It is the responsibility of the caller to
+   ensure that the subject and actor tokens are refreshed on disk at the
+   specified paths. This API is used for experimental purposes for now and may
+   change in the future. */
+typedef struct {
+  const char* sts_endpoint_url;     /* Required. */
+  const char* resource;             /* Optional. */
+  const char* audience;             /* Optional. */
+  const char* scope;                /* Optional. */
+  const char* requested_token_type; /* Optional. */
+  const char* subject_token_path;   /* Required. */
+  const char* subject_token_type;   /* Required. */
+  const char* actor_token_path;     /* Optional. */
+  const char* actor_token_type;     /* Optional. */
+} grpc_sts_credentials_options;
+
+/** Creates an STS credentials following the STS Token Exchanged specifed in the
+   IETF draft https://tools.ietf.org/html/draft-ietf-oauth-token-exchange-16.
+   This API is used for experimental purposes for now and may change in the
+   future. */
+GRPCAPI grpc_call_credentials* grpc_sts_credentials_create(
+    const grpc_sts_credentials_options* options, void* reserved);
+
 /** Callback function to be called by the metadata credentials plugin
    implementation when the metadata is ready.
    - user_data is the opaque pointer that was passed in the get_metadata method

src/core/lib/security/credentials/jwt/json_token.cc

@@ -18,6 +18,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/security/credentials/jwt/json_token.h"
 
 #include <string.h>
@@ -69,6 +70,7 @@ grpc_auth_json_key grpc_auth_json_key_create_from_json(const grpc_json* json) {
   BIO* bio = nullptr;
   const char* prop_value;
   int success = 0;
+  grpc_error* error = GRPC_ERROR_NONE;
 
   memset(&result, 0, sizeof(grpc_auth_json_key));
   result.type = GRPC_AUTH_JSON_TYPE_INVALID;
@@ -77,7 +79,8 @@ grpc_auth_json_key grpc_auth_json_key_create_from_json(const grpc_json* json) {
     goto end;
   }
 
-  prop_value = grpc_json_get_string_property(json, "type");
+  prop_value = grpc_json_get_string_property(json, "type", &error);
+  GRPC_LOG_IF_ERROR("JSON key parsing", error);
   if (prop_value == nullptr ||
       strcmp(prop_value, GRPC_AUTH_JSON_TYPE_SERVICE_ACCOUNT)) {
     goto end;
@@ -92,7 +95,8 @@ grpc_auth_json_key grpc_auth_json_key_create_from_json(const grpc_json* json) {
     goto end;
   }
 
-  prop_value = grpc_json_get_string_property(json, "private_key");
+  prop_value = grpc_json_get_string_property(json, "private_key", &error);
+  GRPC_LOG_IF_ERROR("JSON key parsing", error);
   if (prop_value == nullptr) {
     goto end;
   }

src/core/lib/security/credentials/oauth2/oauth2_credentials.cc

@@ -22,14 +22,23 @@
 
 #include <string.h>
 
-#include "src/core/lib/gprpp/ref_counted_ptr.h"
-#include "src/core/lib/security/util/json_util.h"
-#include "src/core/lib/surface/api_trace.h"
-
+#include <grpc/grpc_security.h>
+#include <grpc/impl/codegen/slice.h>
+#include <grpc/slice.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 
+#include "src/core/lib/gpr/string.h"
+#include "src/core/lib/gprpp/inlined_vector.h"
+#include "src/core/lib/gprpp/ref_counted_ptr.h"
+#include "src/core/lib/iomgr/error.h"
+#include "src/core/lib/iomgr/load_file.h"
+#include "src/core/lib/security/util/json_util.h"
+#include "src/core/lib/slice/slice_internal.h"
+#include "src/core/lib/surface/api_trace.h"
+#include "src/core/lib/uri/uri_parser.h"
+
 //
 // Auth Refresh Token.
 //
@@ -45,6 +54,7 @@ grpc_auth_refresh_token grpc_auth_refresh_token_create_from_json(
   grpc_auth_refresh_token result;
   const char* prop_value;
   int success = 0;
+  grpc_error* error = GRPC_ERROR_NONE;
 
   memset(&result, 0, sizeof(grpc_auth_refresh_token));
   result.type = GRPC_AUTH_JSON_TYPE_INVALID;
@@ -53,7 +63,8 @@ grpc_auth_refresh_token grpc_auth_refresh_token_create_from_json(
     goto end;
   }
 
-  prop_value = grpc_json_get_string_property(json, "type");
+  prop_value = grpc_json_get_string_property(json, "type", &error);
+  GRPC_LOG_IF_ERROR("Parsing refresh token", error);
   if (prop_value == nullptr ||
       strcmp(prop_value, GRPC_AUTH_JSON_TYPE_AUTHORIZED_USER)) {
     goto end;
@@ -218,8 +229,10 @@ void grpc_oauth2_token_fetcher_credentials::on_http_response(
   grpc_mdelem access_token_md = GRPC_MDNULL;
   grpc_millis token_lifetime;
   grpc_credentials_status status =
-      grpc_oauth2_token_fetcher_credentials_parse_server_response(
-          &r->response, &access_token_md, &token_lifetime);
+      error == GRPC_ERROR_NONE
+          ? grpc_oauth2_token_fetcher_credentials_parse_server_response(
+                &r->response, &access_token_md, &token_lifetime)
+          : GRPC_CREDENTIALS_ERROR;
   // Update cache and grab list of pending requests.
   gpr_mu_lock(&mu_);
   token_fetch_pending_ = false;
@@ -234,14 +247,15 @@ void grpc_oauth2_token_fetcher_credentials::on_http_response(
   gpr_mu_unlock(&mu_);
   // Invoke callbacks for all pending requests.
   while (pending_request != nullptr) {
+    grpc_error* new_error = GRPC_ERROR_NONE;
     if (status == GRPC_CREDENTIALS_OK) {
       grpc_credentials_mdelem_array_add(pending_request->md_array,
                                         access_token_md);
     } else {
-      error = GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
+      new_error = GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
           "Error occurred when fetching oauth2 token.", &error, 1);
     }
-    GRPC_CLOSURE_SCHED(pending_request->on_request_metadata, error);
+    GRPC_CLOSURE_SCHED(pending_request->on_request_metadata, new_error);
     grpc_polling_entity_del_from_pollset_set(
         pending_request->pollent, grpc_polling_entity_pollset_set(&pollent_));
     grpc_oauth2_pending_get_request_metadata* prev = pending_request;
@@ -356,7 +370,8 @@ class grpc_compute_engine_token_fetcher_credentials
                     grpc_polling_entity* pollent,
                     grpc_iomgr_cb_func response_cb,
                     grpc_millis deadline) override {
-    grpc_http_header header = {(char*)"Metadata-Flavor", (char*)"Google"};
+    grpc_http_header header = {const_cast<char*>("Metadata-Flavor"),
+                               const_cast<char*>("Google")};
     grpc_httpcli_request request;
     memset(&request, 0, sizeof(grpc_httpcli_request));
     request.host = (char*)GRPC_COMPUTE_ENGINE_METADATA_HOST;
@@ -369,11 +384,14 @@ class grpc_compute_engine_token_fetcher_credentials
     grpc_resource_quota* resource_quota =
         grpc_resource_quota_create("oauth2_credentials");
     grpc_httpcli_get(http_context, pollent, resource_quota, &request, deadline,
-                     GRPC_CLOSURE_CREATE(response_cb, metadata_req,
-                                         grpc_schedule_on_exec_ctx),
+                     GRPC_CLOSURE_INIT(&http_get_cb_closure_, response_cb,
+                                       metadata_req, grpc_schedule_on_exec_ctx),
                      &metadata_req->response);
     grpc_resource_quota_unref_internal(resource_quota);
   }
+
+ private:
+  grpc_closure http_get_cb_closure_;
 };
 
 }  // namespace
@@ -401,8 +419,9 @@ void grpc_google_refresh_token_credentials::fetch_oauth2(
     grpc_credentials_metadata_request* metadata_req,
     grpc_httpcli_context* httpcli_context, grpc_polling_entity* pollent,
     grpc_iomgr_cb_func response_cb, grpc_millis deadline) {
-  grpc_http_header header = {(char*)"Content-Type",
-                             (char*)"application/x-www-form-urlencoded"};
+  grpc_http_header header = {
+      const_cast<char*>("Content-Type"),
+      const_cast<char*>("application/x-www-form-urlencoded")};
   grpc_httpcli_request request;
   char* body = nullptr;
   gpr_asprintf(&body, GRPC_REFRESH_TOKEN_POST_BODY_FORMAT_STRING,
@@ -419,11 +438,11 @@ void grpc_google_refresh_token_credentials::fetch_oauth2(
      extreme memory pressure. */
   grpc_resource_quota* resource_quota =
       grpc_resource_quota_create("oauth2_credentials_refresh");
-  grpc_httpcli_post(
-      httpcli_context, pollent, resource_quota, &request, body, strlen(body),
-      deadline,
-      GRPC_CLOSURE_CREATE(response_cb, metadata_req, grpc_schedule_on_exec_ctx),
-      &metadata_req->response);
+  grpc_httpcli_post(httpcli_context, pollent, resource_quota, &request, body,
+                    strlen(body), deadline,
+                    GRPC_CLOSURE_INIT(&http_post_cb_closure_, response_cb,
+                                      metadata_req, grpc_schedule_on_exec_ctx),
+                    &metadata_req->response);
   grpc_resource_quota_unref_internal(resource_quota);
   gpr_free(body);
 }
@@ -472,6 +491,207 @@ grpc_call_credentials* grpc_google_refresh_token_credentials_create(
       .release();
 }
 
+//
+// STS credentials.
+//
+
+namespace grpc_core {
+
+namespace {
+
+void MaybeAddToBody(gpr_strvec* body_strvec, const char* field_name,
+                    const char* field) {
+  if (field == nullptr || strlen(field) == 0) return;
+  char* new_query;
+  gpr_asprintf(&new_query, "&%s=%s", field_name, field);
+  gpr_strvec_add(body_strvec, new_query);
+}
+
+grpc_error* LoadTokenFile(const char* path, gpr_slice* token) {
+  grpc_error* err = grpc_load_file(path, 1, token);
+  if (err != GRPC_ERROR_NONE) return err;
+  if (GRPC_SLICE_LENGTH(*token) == 0) {
+    gpr_log(GPR_ERROR, "Token file %s is empty", path);
+    err = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Token file is empty.");
+  }
+  return err;
+}
+
+class StsTokenFetcherCredentials
+    : public grpc_oauth2_token_fetcher_credentials {
+ public:
+  StsTokenFetcherCredentials(grpc_uri* sts_url,  // Ownership transfered.
+                             const grpc_sts_credentials_options* options)
+      : sts_url_(sts_url),
+        resource_(gpr_strdup(options->resource)),
+        audience_(gpr_strdup(options->audience)),
+        scope_(gpr_strdup(options->scope)),
+        requested_token_type_(gpr_strdup(options->requested_token_type)),
+        subject_token_path_(gpr_strdup(options->subject_token_path)),
+        subject_token_type_(gpr_strdup(options->subject_token_type)),
+        actor_token_path_(gpr_strdup(options->actor_token_path)),
+        actor_token_type_(gpr_strdup(options->actor_token_type)) {}
+
+  ~StsTokenFetcherCredentials() override { grpc_uri_destroy(sts_url_); }
+
+ private:
+  void fetch_oauth2(grpc_credentials_metadata_request* metadata_req,
+                    grpc_httpcli_context* http_context,
+                    grpc_polling_entity* pollent,
+                    grpc_iomgr_cb_func response_cb,
+                    grpc_millis deadline) override {
+    char* body = nullptr;
+    size_t body_length = 0;
+    grpc_error* err = FillBody(&body, &body_length);
+    if (err != GRPC_ERROR_NONE) {
+      response_cb(metadata_req, err);
+      GRPC_ERROR_UNREF(err);
+      return;
+    }
+    grpc_http_header header = {
+        const_cast<char*>("Content-Type"),
+        const_cast<char*>("application/x-www-form-urlencoded")};
+    grpc_httpcli_request request;
+    memset(&request, 0, sizeof(grpc_httpcli_request));
+    request.host = (char*)sts_url_->authority;
+    request.http.path = (char*)sts_url_->path;
+    request.http.hdr_count = 1;
+    request.http.hdrs = &header;
+    request.handshaker = (strcmp(sts_url_->scheme, "https") == 0)
+                             ? &grpc_httpcli_ssl
+                             : &grpc_httpcli_plaintext;
+    /* TODO(ctiller): Carry the resource_quota in ctx and share it with the host
+       channel. This would allow us to cancel an authentication query when under
+       extreme memory pressure. */
+    grpc_resource_quota* resource_quota =
+        grpc_resource_quota_create("oauth2_credentials_refresh");
+    grpc_httpcli_post(
+        http_context, pollent, resource_quota, &request, body, body_length,
+        deadline,
+        GRPC_CLOSURE_INIT(&http_post_cb_closure_, response_cb, metadata_req,
+                          grpc_schedule_on_exec_ctx),
+        &metadata_req->response);
+    grpc_resource_quota_unref_internal(resource_quota);
+    gpr_free(body);
+  }
+
+  grpc_error* FillBody(char** body, size_t* body_length) {
+    *body = nullptr;
+    gpr_strvec body_strvec;
+    gpr_strvec_init(&body_strvec);
+    grpc_slice subject_token = grpc_empty_slice();
+    grpc_slice actor_token = grpc_empty_slice();
+    grpc_error* err = GRPC_ERROR_NONE;
+
+    auto cleanup = [&body, &body_length, &body_strvec, &subject_token,
+                    &actor_token, &err]() {
+      if (err == GRPC_ERROR_NONE) {
+        *body = gpr_strvec_flatten(&body_strvec, body_length);
+      } else {
+        gpr_free(*body);
+      }
+      gpr_strvec_destroy(&body_strvec);
+      grpc_slice_unref_internal(subject_token);
+      grpc_slice_unref_internal(actor_token);
+      return err;
+    };
+
+    err = LoadTokenFile(subject_token_path_.get(), &subject_token);
+    if (err != GRPC_ERROR_NONE) return cleanup();
+    gpr_asprintf(
+        body, GRPC_STS_POST_MINIMAL_BODY_FORMAT_STRING,
+        reinterpret_cast<const char*>(GRPC_SLICE_START_PTR(subject_token)),
+        subject_token_type_.get());
+    gpr_strvec_add(&body_strvec, *body);
+    MaybeAddToBody(&body_strvec, "resource", resource_.get());
+    MaybeAddToBody(&body_strvec, "audience", audience_.get());
+    MaybeAddToBody(&body_strvec, "scope", scope_.get());
+    MaybeAddToBody(&body_strvec, "requested_token_type",
+                   requested_token_type_.get());
+    if (actor_token_path_ != nullptr) {
+      err = LoadTokenFile(actor_token_path_.get(), &actor_token);
+      if (err != GRPC_ERROR_NONE) return cleanup();
+      MaybeAddToBody(
+          &body_strvec, "actor_token",
+          reinterpret_cast<const char*>(GRPC_SLICE_START_PTR(subject_token)));
+      MaybeAddToBody(&body_strvec, "actor_token_type", actor_token_type_.get());
+    }
+    return cleanup();
+  }
+
+  grpc_uri* sts_url_;
+  grpc_closure http_post_cb_closure_;
+  grpc_core::UniquePtr<char> resource_;
+  grpc_core::UniquePtr<char> audience_;
+  grpc_core::UniquePtr<char> scope_;
+  grpc_core::UniquePtr<char> requested_token_type_;
+  grpc_core::UniquePtr<char> subject_token_path_;
+  grpc_core::UniquePtr<char> subject_token_type_;
+  grpc_core::UniquePtr<char> actor_token_path_;
+  grpc_core::UniquePtr<char> actor_token_type_;
+};
+
+}  // namespace
+
+grpc_error* ValidateStsCredentialsOptions(
+    const grpc_sts_credentials_options* options, grpc_uri** sts_url_out) {
+  struct GrpcUriDeleter {
+    void operator()(grpc_uri* uri) { grpc_uri_destroy(uri); }
+  };
+  *sts_url_out = nullptr;
+  InlinedVector<grpc_error*, 3> error_list;
+  UniquePtr<grpc_uri, GrpcUriDeleter> sts_url(
+      options->sts_endpoint_url != nullptr
+          ? grpc_uri_parse(options->sts_endpoint_url, false)
+          : nullptr);
+  if (sts_url == nullptr) {
+    error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+        "Invalid or missing STS endpoint URL"));
+  } else {
+    if (strcmp(sts_url->scheme, "https") != 0 &&
+        strcmp(sts_url->scheme, "http") != 0) {
+      error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+          "Invalid URI scheme, must be https to http."));
+    }
+  }
+  if (options->subject_token_path == nullptr ||
+      strlen(options->subject_token_path) == 0) {
+    error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+        "subject_token needs to be specified"));
+  }
+  if (options->subject_token_type == nullptr ||
+      strlen(options->subject_token_type) == 0) {
+    error_list.push_back(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+        "subject_token_type needs to be specified"));
+  }
+  if (error_list.empty()) {
+    *sts_url_out = sts_url.release();
+    return GRPC_ERROR_NONE;
+  } else {
+    return GRPC_ERROR_CREATE_FROM_VECTOR("Invalid STS Credentials Options",
+                                         &error_list);
+  }
+}
+
+}  // namespace grpc_core
+
+grpc_call_credentials* grpc_sts_credentials_create(
+    const grpc_sts_credentials_options* options, void* reserved) {
+  GPR_ASSERT(reserved == nullptr);
+  grpc_uri* sts_url;
+  grpc_error* error =
+      grpc_core::ValidateStsCredentialsOptions(options, &sts_url);
+  if (error != GRPC_ERROR_NONE) {
+    gpr_log(GPR_ERROR, "STS Credentials creation failed. Error: %s.",
+            grpc_error_string(error));
+    GRPC_ERROR_UNREF(error);
+    return nullptr;
+  }
+  return grpc_core::MakeRefCounted<grpc_core::StsTokenFetcherCredentials>(
+             sts_url, options)
+      .release();
+}
+
 //
 // Oauth2 Access Token credentials.
 //

src/core/lib/security/credentials/oauth2/oauth2_credentials.h

@@ -21,8 +21,15 @@
 
 #include <grpc/support/port_platform.h>
 
+#include <grpc/grpc_security.h>
 #include "src/core/lib/json/json.h"
 #include "src/core/lib/security/credentials/credentials.h"
+#include "src/core/lib/uri/uri_parser.h"
+
+// Constants.
+#define GRPC_STS_POST_MINIMAL_BODY_FORMAT_STRING                               \
+  "grant_type=urn:ietf:params:oauth:grant-type:token-exchange&subject_token=%" \
+  "s&subject_token_type=%s"
 
 // auth_refresh_token parsing.
 typedef struct {
@@ -115,6 +122,7 @@ class grpc_google_refresh_token_credentials final
 
  private:
   grpc_auth_refresh_token refresh_token_;
+  grpc_closure http_post_cb_closure_;
 };
 
 // Access token credentials.
@@ -148,4 +156,12 @@ grpc_oauth2_token_fetcher_credentials_parse_server_response(
     const struct grpc_http_response* response, grpc_mdelem* token_md,
     grpc_millis* token_lifetime);
 
+namespace grpc_core {
+// Exposed for testing only. This function validates the options, ensuring that
+// the required fields are set, and outputs the parsed URL of the STS token
+// exchanged service.
+grpc_error* ValidateStsCredentialsOptions(
+    const grpc_sts_credentials_options* options, grpc_uri** sts_url);
+}  // namespace grpc_core
+
 #endif /* GRPC_CORE_LIB_SECURITY_CREDENTIALS_OAUTH2_OAUTH2_CREDENTIALS_H */

src/core/lib/security/util/json_util.cc

@@ -18,6 +18,7 @@
 
 #include <grpc/support/port_platform.h>
 
+#include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/security/util/json_util.h"
 
 #include <string.h>
@@ -26,17 +27,27 @@
 #include <grpc/support/string_util.h>
 
 const char* grpc_json_get_string_property(const grpc_json* json,
-                                          const char* prop_name) {
-  grpc_json* child;
+                                          const char* prop_name,
+                                          grpc_error** error) {
+  grpc_json* child = nullptr;
+  if (error != nullptr) *error = GRPC_ERROR_NONE;
   for (child = json->child; child != nullptr; child = child->next) {
     if (child->key == nullptr) {
-      gpr_log(GPR_ERROR, "Invalid (null) JSON key encountered");
+      if (error != nullptr) {
+        *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+            "Invalid (null) JSON key encountered");
+      }
       return nullptr;
     }
     if (strcmp(child->key, prop_name) == 0) break;
   }
   if (child == nullptr || child->type != GRPC_JSON_STRING) {
-    gpr_log(GPR_ERROR, "Invalid or missing %s property.", prop_name);
+    if (error != nullptr) {
+      char* error_msg;
+      gpr_asprintf(&error_msg, "Invalid or missing %s property.", prop_name);
+      *error = GRPC_ERROR_CREATE_FROM_COPIED_STRING(error_msg);
+      gpr_free(error_msg);
+    }
     return nullptr;
   }
   return child->value;
@@ -45,7 +56,10 @@ const char* grpc_json_get_string_property(const grpc_json* json,
 bool grpc_copy_json_string_property(const grpc_json* json,
                                     const char* prop_name,
                                     char** copied_value) {
-  const char* prop_value = grpc_json_get_string_property(json, prop_name);
+  grpc_error* error = GRPC_ERROR_NONE;
+  const char* prop_value =
+      grpc_json_get_string_property(json, prop_name, &error);
+  GRPC_LOG_IF_ERROR("Could not copy JSON property", error);
   if (prop_value == nullptr) return false;
   *copied_value = gpr_strdup(prop_value);
   return true;

src/core/lib/security/util/json_util.h

@@ -23,6 +23,7 @@
 
 #include <stdbool.h>
 
+#include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/json/json.h"
 
 // Constants.
@@ -32,7 +33,8 @@
 
 // Gets a child property from a json node.
 const char* grpc_json_get_string_property(const grpc_json* json,
-                                          const char* prop_name);
+                                          const char* prop_name,
+                                          grpc_error** error);
 
 // Copies the value of the json child property specified by prop_name.
 // Returns false if the property was not found.

src/ruby/ext/grpc/rb_grpc_imports.generated.c

@@ -134,6 +134,7 @@ grpc_service_account_jwt_access_credentials_create_type grpc_service_account_jwt
 grpc_google_refresh_token_credentials_create_type grpc_google_refresh_token_credentials_create_import;
 grpc_access_token_credentials_create_type grpc_access_token_credentials_create_import;
 grpc_google_iam_credentials_create_type grpc_google_iam_credentials_create_import;
+grpc_sts_credentials_create_type grpc_sts_credentials_create_import;
 grpc_metadata_credentials_create_from_plugin_type grpc_metadata_credentials_create_from_plugin_import;
 grpc_secure_channel_create_type grpc_secure_channel_create_import;
 grpc_server_credentials_release_type grpc_server_credentials_release_import;
@@ -404,6 +405,7 @@ void grpc_rb_load_imports(HMODULE library) {
   grpc_google_refresh_token_credentials_create_import = (grpc_google_refresh_token_credentials_create_type) GetProcAddress(library, "grpc_google_refresh_token_credentials_create");
   grpc_access_token_credentials_create_import = (grpc_access_token_credentials_create_type) GetProcAddress(library, "grpc_access_token_credentials_create");
   grpc_google_iam_credentials_create_import = (grpc_google_iam_credentials_create_type) GetProcAddress(library, "grpc_google_iam_credentials_create");
+  grpc_sts_credentials_create_import = (grpc_sts_credentials_create_type) GetProcAddress(library, "grpc_sts_credentials_create");
   grpc_metadata_credentials_create_from_plugin_import = (grpc_metadata_credentials_create_from_plugin_type) GetProcAddress(library, "grpc_metadata_credentials_create_from_plugin");
   grpc_secure_channel_create_import = (grpc_secure_channel_create_type) GetProcAddress(library, "grpc_secure_channel_create");
   grpc_server_credentials_release_import = (grpc_server_credentials_release_type) GetProcAddress(library, "grpc_server_credentials_release");

src/ruby/ext/grpc/rb_grpc_imports.generated.h

@@ -377,6 +377,9 @@ extern grpc_access_token_credentials_create_type grpc_access_token_credentials_c
 typedef grpc_call_credentials*(*grpc_google_iam_credentials_create_type)(const char* authorization_token, const char* authority_selector, void* reserved);
 extern grpc_google_iam_credentials_create_type grpc_google_iam_credentials_create_import;
 #define grpc_google_iam_credentials_create grpc_google_iam_credentials_create_import
+typedef grpc_call_credentials*(*grpc_sts_credentials_create_type)(const grpc_sts_credentials_options* options, void* reserved);
+extern grpc_sts_credentials_create_type grpc_sts_credentials_create_import;
+#define grpc_sts_credentials_create grpc_sts_credentials_create_import
 typedef grpc_call_credentials*(*grpc_metadata_credentials_create_from_plugin_type)(grpc_metadata_credentials_plugin plugin, void* reserved);
 extern grpc_metadata_credentials_create_from_plugin_type grpc_metadata_credentials_create_from_plugin_import;
 #define grpc_metadata_credentials_create_from_plugin grpc_metadata_credentials_create_from_plugin_import

test/core/security/credentials_test.cc

@@ -24,8 +24,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include <grpc/grpc_security.h>
 #include <grpc/slice.h>
-
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
@@ -34,13 +34,16 @@
 #include "src/core/lib/gpr/env.h"
 #include "src/core/lib/gpr/string.h"
 #include "src/core/lib/gpr/tmpfile.h"
+#include "src/core/lib/gprpp/host_port.h"
 #include "src/core/lib/http/httpcli.h"
+#include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/security/credentials/composite/composite_credentials.h"
 #include "src/core/lib/security/credentials/fake/fake_credentials.h"
 #include "src/core/lib/security/credentials/google_default/google_default_credentials.h"
 #include "src/core/lib/security/credentials/jwt/jwt_credentials.h"
 #include "src/core/lib/security/credentials/oauth2/oauth2_credentials.h"
 #include "src/core/lib/security/transport/auth_filters.h"
+#include "src/core/lib/uri/uri_parser.h"
 #include "test/core/util/test_config.h"
 
 using grpc_core::internal::grpc_flush_cached_google_default_credentials;
@@ -99,15 +102,27 @@ static const char valid_oauth2_json_response[] =
     " \"expires_in\":3599, "
     " \"token_type\":\"Bearer\"}";
 
+static const char valid_sts_json_response[] =
+    "{\"access_token\":\"ya29.AHES6ZRN3-HlhAPya30GnW_bHSb_\","
+    " \"expires_in\":3599, "
+    " \"issued_token_type\":\"urn:ietf:params:oauth:token-type:access_token\", "
+    " \"token_type\":\"Bearer\"}";
+
 static const char test_scope[] = "perm1 perm2";
 
 static const char test_signed_jwt[] =
     "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImY0OTRkN2M1YWU2MGRmOTcyNmM4YW"
     "U0MDcyZTViYTdmZDkwODg2YzcifQ";
+static const char test_signed_jwt_token_type[] =
+    "urn:ietf:params:oauth:token-type:id_token";
+static const char test_signed_jwt_path_prefix[] = "test_sign_jwt";
 
 static const char test_service_url[] = "https://foo.com/foo.v1";
 static const char other_test_service_url[] = "https://bar.com/bar.v1";
 
+static const char test_sts_endpoint_url[] =
+    "https://foo.com:5555/v1/token-exchange";
+
 static const char test_method[] = "ThisIsNotAMethod";
 
 /*  -- Global state flags. -- */
@@ -657,11 +672,11 @@ static int refresh_token_httpcli_post_success(
   return 1;
 }
 
-static int refresh_token_httpcli_post_failure(
-    const grpc_httpcli_request* request, const char* body, size_t body_size,
-    grpc_millis deadline, grpc_closure* on_done,
-    grpc_httpcli_response* response) {
-  validate_refresh_token_http_request(request, body, body_size);
+static int token_httpcli_post_failure(const grpc_httpcli_request* request,
+                                      const char* body, size_t body_size,
+                                      grpc_millis deadline,
+                                      grpc_closure* on_done,
+                                      grpc_httpcli_response* response) {
   *response = http_response(403, "Not Authorized.");
   GRPC_CLOSURE_SCHED(on_done, GRPC_ERROR_NONE);
   return 1;
@@ -676,7 +691,7 @@ static void test_refresh_token_creds_success(void) {
   grpc_call_credentials* creds = grpc_google_refresh_token_credentials_create(
       test_refresh_token_str, nullptr);
 
-  /* First request: http get should be called. */
+  /* First request: http put should be called. */
   request_metadata_state* state =
       make_request_metadata_state(GRPC_ERROR_NONE, emd, GPR_ARRAY_SIZE(emd));
   grpc_httpcli_set_override(httpcli_get_should_not_be_called,
@@ -707,10 +722,279 @@ static void test_refresh_token_creds_failure(void) {
   grpc_call_credentials* creds = grpc_google_refresh_token_credentials_create(
       test_refresh_token_str, nullptr);
   grpc_httpcli_set_override(httpcli_get_should_not_be_called,
-                            refresh_token_httpcli_post_failure);
+                            token_httpcli_post_failure);
+  run_request_metadata_test(creds, auth_md_ctx, state);
+  creds->Unref();
+  grpc_httpcli_set_override(nullptr, nullptr);
+}
+
+static void test_valid_sts_creds_options(void) {
+  grpc_sts_credentials_options valid_options = {
+      test_sts_endpoint_url,        // sts_endpoint_url
+      nullptr,                      // resource
+      nullptr,                      // audience
+      nullptr,                      // scope
+      nullptr,                      // requested_token_type
+      test_signed_jwt_path_prefix,  // subject_token_path
+      test_signed_jwt_token_type,   // subject_token_type
+      nullptr,                      // actor_token_path
+      nullptr                       // actor_token_type
+  };
+  grpc_uri* sts_url;
+  grpc_error* error =
+      grpc_core::ValidateStsCredentialsOptions(&valid_options, &sts_url);
+  GPR_ASSERT(error == GRPC_ERROR_NONE);
+  GPR_ASSERT(sts_url != nullptr);
+  grpc_core::StringView host;
+  grpc_core::StringView port;
+  GPR_ASSERT(grpc_core::SplitHostPort(sts_url->authority, &host, &port));
+  GPR_ASSERT(host.cmp("foo.com") == 0);
+  GPR_ASSERT(port.cmp("5555") == 0);
+  grpc_uri_destroy(sts_url);
+}
+
+static void test_invalid_sts_creds_options(void) {
+  grpc_sts_credentials_options invalid_options = {
+      test_sts_endpoint_url,       // sts_endpoint_url
+      nullptr,                     // resource
+      nullptr,                     // audience
+      nullptr,                     // scope
+      nullptr,                     // requested_token_type
+      nullptr,                     // subject_token_path (Required)
+      test_signed_jwt_token_type,  // subject_token_type
+      nullptr,                     // actor_token_path
+      nullptr                      // actor_token_type
+  };
+  grpc_uri* url_should_be_null;
+  grpc_error* error = grpc_core::ValidateStsCredentialsOptions(
+      &invalid_options, &url_should_be_null);
+  GPR_ASSERT(error != GRPC_ERROR_NONE);
+  GRPC_ERROR_UNREF(error);
+  GPR_ASSERT(url_should_be_null == nullptr);
+
+  invalid_options = {
+      test_sts_endpoint_url,        // sts_endpoint_url
+      nullptr,                      // resource
+      nullptr,                      // audience
+      nullptr,                      // scope
+      nullptr,                      // requested_token_type
+      test_signed_jwt_path_prefix,  // subject_token_path
+      nullptr,                      // subject_token_type (Required)
+      nullptr,                      // actor_token_path
+      nullptr                       // actor_token_type
+  };
+  error = grpc_core::ValidateStsCredentialsOptions(&invalid_options,
+                                                   &url_should_be_null);
+  GPR_ASSERT(error != GRPC_ERROR_NONE);
+  GRPC_ERROR_UNREF(error);
+  GPR_ASSERT(url_should_be_null == nullptr);
+
+  invalid_options = {
+      nullptr,                      // sts_endpoint_url (Required)
+      nullptr,                      // resource
+      nullptr,                      // audience
+      nullptr,                      // scope
+      nullptr,                      // requested_token_type
+      test_signed_jwt_path_prefix,  // subject_token_path
+      test_signed_jwt_token_type,   // subject_token_type (Required)
+      nullptr,                      // actor_token_path
+      nullptr                       // actor_token_type
+  };
+  error = grpc_core::ValidateStsCredentialsOptions(&invalid_options,
+                                                   &url_should_be_null);
+  GPR_ASSERT(error != GRPC_ERROR_NONE);
+  GRPC_ERROR_UNREF(error);
+  GPR_ASSERT(url_should_be_null == nullptr);
+
+  invalid_options = {
+      "not_a_valid_uri",            // sts_endpoint_url
+      nullptr,                      // resource
+      nullptr,                      // audience
+      nullptr,                      // scope
+      nullptr,                      // requested_token_type
+      test_signed_jwt_path_prefix,  // subject_token_path
+      test_signed_jwt_token_type,   // subject_token_type (Required)
+      nullptr,                      // actor_token_path
+      nullptr                       // actor_token_type
+  };
+  error = grpc_core::ValidateStsCredentialsOptions(&invalid_options,
+                                                   &url_should_be_null);
+  GPR_ASSERT(error != GRPC_ERROR_NONE);
+  GRPC_ERROR_UNREF(error);
+  GPR_ASSERT(url_should_be_null == nullptr);
+
+  invalid_options = {
+      "ftp://ftp.is.not.a.valid.scheme/bar",  // sts_endpoint_url
+      nullptr,                                // resource
+      nullptr,                                // audience
+      nullptr,                                // scope
+      nullptr,                                // requested_token_type
+      test_signed_jwt_path_prefix,            // subject_token_path
+      test_signed_jwt_token_type,             // subject_token_type (Required)
+      nullptr,                                // actor_token_path
+      nullptr                                 // actor_token_type
+  };
+  error = grpc_core::ValidateStsCredentialsOptions(&invalid_options,
+                                                   &url_should_be_null);
+  GPR_ASSERT(error != GRPC_ERROR_NONE);
+  GRPC_ERROR_UNREF(error);
+  GPR_ASSERT(url_should_be_null == nullptr);
+}
+
+static void validate_sts_token_http_request(const grpc_httpcli_request* request,
+                                            const char* body,
+                                            size_t body_size) {
+  // Check that the body is constructed properly.
+  GPR_ASSERT(body != nullptr);
+  GPR_ASSERT(body_size != 0);
+  GPR_ASSERT(request->handshaker == &grpc_httpcli_ssl);
+  char* get_url_equivalent;
+  gpr_asprintf(&get_url_equivalent, "%s?%s", test_sts_endpoint_url, body);
+  grpc_uri* url = grpc_uri_parse(get_url_equivalent, false);
+  GPR_ASSERT(strcmp(grpc_uri_get_query_arg(url, "resource"), "resource") == 0);
+  GPR_ASSERT(strcmp(grpc_uri_get_query_arg(url, "audience"), "audience") == 0);
+  GPR_ASSERT(strcmp(grpc_uri_get_query_arg(url, "scope"), "scope") == 0);
+  GPR_ASSERT(strcmp(grpc_uri_get_query_arg(url, "requested_token_type"),
+                    "requested_token_type") == 0);
+  GPR_ASSERT(strcmp(grpc_uri_get_query_arg(url, "subject_token"),
+                    test_signed_jwt) == 0);
+  GPR_ASSERT(strcmp(grpc_uri_get_query_arg(url, "subject_token_type"),
+                    test_signed_jwt_token_type) == 0);
+  GPR_ASSERT(grpc_uri_get_query_arg(url, "actor_token") == nullptr);
+  GPR_ASSERT(grpc_uri_get_query_arg(url, "actor_token_type") == nullptr);
+  grpc_uri_destroy(url);
+  gpr_free(get_url_equivalent);
+
+  // Check the rest of the request.
+  GPR_ASSERT(strcmp(request->host, "foo.com:5555") == 0);
+  GPR_ASSERT(strcmp(request->http.path, "/v1/token-exchange") == 0);
+  GPR_ASSERT(request->http.hdr_count == 1);
+  GPR_ASSERT(strcmp(request->http.hdrs[0].key, "Content-Type") == 0);
+  GPR_ASSERT(strcmp(request->http.hdrs[0].value,
+                    "application/x-www-form-urlencoded") == 0);
+}
+
+static int sts_token_httpcli_post_success(const grpc_httpcli_request* request,
+                                          const char* body, size_t body_size,
+                                          grpc_millis deadline,
+                                          grpc_closure* on_done,
+                                          grpc_httpcli_response* response) {
+  validate_sts_token_http_request(request, body, body_size);
+  *response = http_response(200, valid_sts_json_response);
+  GRPC_CLOSURE_SCHED(on_done, GRPC_ERROR_NONE);
+  return 1;
+}
+
+static char* write_tmp_jwt_file(void) {
+  char* path;
+  FILE* tmp = gpr_tmpfile(test_signed_jwt_path_prefix, &path);
+  GPR_ASSERT(path != nullptr);
+  GPR_ASSERT(tmp != nullptr);
+  size_t jwt_length = strlen(test_signed_jwt);
+  GPR_ASSERT(fwrite(test_signed_jwt, 1, jwt_length, tmp) == jwt_length);
+  fclose(tmp);
+  return path;
+}
+
+static void test_sts_creds_success(void) {
+  grpc_core::ExecCtx exec_ctx;
+  expected_md emd[] = {
+      {"authorization", "Bearer ya29.AHES6ZRN3-HlhAPya30GnW_bHSb_"}};
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method,
+                                            nullptr, nullptr};
+  char* test_signed_jwt_path = write_tmp_jwt_file();
+  grpc_sts_credentials_options valid_options = {
+      test_sts_endpoint_url,       // sts_endpoint_url
+      "resource",                  // resource
+      "audience",                  // audience
+      "scope",                     // scope
+      "requested_token_type",      // requested_token_type
+      test_signed_jwt_path,        // subject_token_path
+      test_signed_jwt_token_type,  // subject_token_type
+      nullptr,                     // actor_token_path
+      nullptr                      // actor_token_type
+  };
+  grpc_call_credentials* creds =
+      grpc_sts_credentials_create(&valid_options, nullptr);
+
+  /* First request: http put should be called. */
+  request_metadata_state* state =
+      make_request_metadata_state(GRPC_ERROR_NONE, emd, GPR_ARRAY_SIZE(emd));
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            sts_token_httpcli_post_success);
+  run_request_metadata_test(creds, auth_md_ctx, state);
+  grpc_core::ExecCtx::Get()->Flush();
+
+  /* Second request: the cached token should be served directly. */
+  state =
+      make_request_metadata_state(GRPC_ERROR_NONE, emd, GPR_ARRAY_SIZE(emd));
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            httpcli_post_should_not_be_called);
+  run_request_metadata_test(creds, auth_md_ctx, state);
+  grpc_core::ExecCtx::Get()->Flush();
+
+  creds->Unref();
+  grpc_httpcli_set_override(nullptr, nullptr);
+  gpr_free(test_signed_jwt_path);
+}
+
+static void test_sts_creds_load_token_failure(void) {
+  grpc_core::ExecCtx exec_ctx;
+  request_metadata_state* state = make_request_metadata_state(
+      GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+          "Error occurred when fetching oauth2 token."),
+      nullptr, 0);
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method,
+                                            nullptr, nullptr};
+  char* test_signed_jwt_path = write_tmp_jwt_file();
+  grpc_sts_credentials_options options = {
+      test_sts_endpoint_url,       // sts_endpoint_url
+      "resource",                  // resource
+      "audience",                  // audience
+      "scope",                     // scope
+      "requested_token_type",      // requested_token_type
+      "invalid_path",              // subject_token_path
+      test_signed_jwt_token_type,  // subject_token_type
+      nullptr,                     // actor_token_path
+      nullptr                      // actor_token_type
+  };
+  grpc_call_credentials* creds = grpc_sts_credentials_create(&options, nullptr);
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            httpcli_post_should_not_be_called);
+  run_request_metadata_test(creds, auth_md_ctx, state);
+  creds->Unref();
+  grpc_httpcli_set_override(nullptr, nullptr);
+  gpr_free(test_signed_jwt_path);
+}
+
+static void test_sts_creds_http_failure(void) {
+  grpc_core::ExecCtx exec_ctx;
+  request_metadata_state* state = make_request_metadata_state(
+      GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+          "Error occurred when fetching oauth2 token."),
+      nullptr, 0);
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method,
+                                            nullptr, nullptr};
+  char* test_signed_jwt_path = write_tmp_jwt_file();
+  grpc_sts_credentials_options valid_options = {
+      test_sts_endpoint_url,       // sts_endpoint_url
+      "resource",                  // resource
+      "audience",                  // audience
+      "scope",                     // scope
+      "requested_token_type",      // requested_token_type
+      test_signed_jwt_path,        // subject_token_path
+      test_signed_jwt_token_type,  // subject_token_type
+      nullptr,                     // actor_token_path
+      nullptr                      // actor_token_type
+  };
+  grpc_call_credentials* creds =
+      grpc_sts_credentials_create(&valid_options, nullptr);
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            token_httpcli_post_failure);
   run_request_metadata_test(creds, auth_md_ctx, state);
   creds->Unref();
   grpc_httpcli_set_override(nullptr, nullptr);
+  gpr_free(test_signed_jwt_path);
 }
 
 static void validate_jwt_encode_and_sign_params(
@@ -1288,6 +1572,11 @@ int main(int argc, char** argv) {
   test_compute_engine_creds_failure();
   test_refresh_token_creds_success();
   test_refresh_token_creds_failure();
+  test_valid_sts_creds_options();
+  test_invalid_sts_creds_options();
+  test_sts_creds_success();
+  test_sts_creds_load_token_failure();
+  test_sts_creds_http_failure();
   test_jwt_creds_lifetime();
   test_jwt_creds_success();
   test_jwt_creds_signing_failure();

test/core/security/fetch_oauth2.cc

@@ -26,33 +26,82 @@
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
 
+#include "src/core/lib/iomgr/error.h"
 #include "src/core/lib/iomgr/load_file.h"
 #include "src/core/lib/security/credentials/credentials.h"
+#include "src/core/lib/security/util/json_util.h"
 #include "test/core/security/oauth2_utils.h"
 #include "test/core/util/cmdline.h"
 
+static grpc_sts_credentials_options sts_options_from_json(grpc_json* json) {
+  grpc_sts_credentials_options options;
+  memset(&options, 0, sizeof(options));
+  grpc_error* error = GRPC_ERROR_NONE;
+  options.sts_endpoint_url =
+      grpc_json_get_string_property(json, "sts_endpoint_url", &error);
+  GRPC_LOG_IF_ERROR("STS credentials parsing", error);
+  options.resource = grpc_json_get_string_property(json, "resource", nullptr);
+  options.audience = grpc_json_get_string_property(json, "audience", nullptr);
+  options.scope = grpc_json_get_string_property(json, "scope", nullptr);
+  options.requested_token_type =
+      grpc_json_get_string_property(json, "requested_token_type", nullptr);
+  options.subject_token_path =
+      grpc_json_get_string_property(json, "subject_token_path", &error);
+  GRPC_LOG_IF_ERROR("STS credentials parsing", error);
+  options.subject_token_type =
+      grpc_json_get_string_property(json, "subject_token_type", &error);
+  GRPC_LOG_IF_ERROR("STS credentials parsing", error);
+  options.actor_token_path =
+      grpc_json_get_string_property(json, "actor_token_path", nullptr);
+  options.actor_token_type =
+      grpc_json_get_string_property(json, "actor_token_type", nullptr);
+  return options;
+}
+
+static grpc_call_credentials* create_sts_creds(const char* json_file_path) {
+  grpc_slice sts_options_slice;
+  GPR_ASSERT(GRPC_LOG_IF_ERROR(
+      "load_file", grpc_load_file(json_file_path, 1, &sts_options_slice)));
+  grpc_json* json = grpc_json_parse_string(
+      reinterpret_cast<char*>(GRPC_SLICE_START_PTR(sts_options_slice)));
+  if (json == nullptr) {
+    gpr_log(GPR_ERROR, "Invalid json");
+    return nullptr;
+  }
+  grpc_sts_credentials_options options = sts_options_from_json(json);
+  grpc_call_credentials* result =
+      grpc_sts_credentials_create(&options, nullptr);
+  grpc_json_destroy(json);
+  gpr_slice_unref(sts_options_slice);
+  return result;
+}
+
 static grpc_call_credentials* create_refresh_token_creds(
     const char* json_refresh_token_file_path) {
   grpc_slice refresh_token;
   GPR_ASSERT(GRPC_LOG_IF_ERROR(
       "load_file",
       grpc_load_file(json_refresh_token_file_path, 1, &refresh_token)));
-  return grpc_google_refresh_token_credentials_create(
+  grpc_call_credentials* result = grpc_google_refresh_token_credentials_create(
       reinterpret_cast<const char*> GRPC_SLICE_START_PTR(refresh_token),
       nullptr);
+  gpr_slice_unref(refresh_token);
+  return result;
 }
 
 int main(int argc, char** argv) {
   grpc_call_credentials* creds = nullptr;
-  char* json_key_file_path = nullptr;
+  const char* json_sts_options_file_path = nullptr;
   const char* json_refresh_token_file_path = nullptr;
   char* token = nullptr;
   int use_gce = 0;
-  char* scope = nullptr;
   gpr_cmdline* cl = gpr_cmdline_create("fetch_oauth2");
   gpr_cmdline_add_string(cl, "json_refresh_token",
                          "File path of the json refresh token.",
                          &json_refresh_token_file_path);
+  gpr_cmdline_add_string(cl, "json_sts_options",
+                         "File path of the json sts options.",
+                         &json_sts_options_file_path);
   gpr_cmdline_add_flag(
       cl, "gce",
       "Get a token from the GCE metadata server (only works in GCE).",
@@ -61,18 +110,20 @@ int main(int argc, char** argv) {
 
   grpc_init();
 
-  if (json_key_file_path != nullptr &&
+  if (json_sts_options_file_path != nullptr &&
       json_refresh_token_file_path != nullptr) {
-    gpr_log(GPR_ERROR,
-            "--json_key and --json_refresh_token are mutually exclusive.");
+    gpr_log(
+        GPR_ERROR,
+        "--json_sts_options and --json_refresh_token are mutually exclusive.");
     exit(1);
   }
 
   if (use_gce) {
-    if (json_key_file_path != nullptr || scope != nullptr) {
+    if (json_sts_options_file_path != nullptr ||
+        json_refresh_token_file_path != nullptr) {
       gpr_log(GPR_INFO,
-              "Ignoring json key and scope to get a token from the GCE "
-              "metadata server.");
+              "Ignoring json refresh token or sts options to get a token from "
+              "the GCE metadata server.");
     }
     creds = grpc_google_compute_engine_credentials_create(nullptr);
     if (creds == nullptr) {
@@ -88,8 +139,19 @@ int main(int argc, char** argv) {
               json_refresh_token_file_path);
       exit(1);
     }
+  } else if (json_sts_options_file_path != nullptr) {
+    creds = create_sts_creds(json_sts_options_file_path);
+    if (creds == nullptr) {
+      gpr_log(GPR_ERROR,
+              "Could not create sts creds. %s does probably not contain a "
+              "valid json for sts options.",
+              json_sts_options_file_path);
+      exit(1);
+    }
   } else {
-    gpr_log(GPR_ERROR, "Missing --gce or --json_refresh_token option.");
+    gpr_log(
+        GPR_ERROR,
+        "Missing --gce, --json_sts_options, or --json_refresh_token option.");
     exit(1);
   }
   GPR_ASSERT(creds != nullptr);

test/core/security/oauth2_utils.cc

@@ -63,14 +63,17 @@ static void on_oauth2_response(void* arg, grpc_error* error) {
   gpr_mu_unlock(request->mu);
 }
 
-static void do_nothing(void* unused, grpc_error* error) {}
+static void destroy_after_shutdown(void* pollset, grpc_error* error) {
+  grpc_pollset_destroy(reinterpret_cast<grpc_pollset*>(pollset));
+  gpr_free(pollset);
+}
 
 char* grpc_test_fetch_oauth2_token_with_credentials(
     grpc_call_credentials* creds) {
   oauth2_request request;
   memset(&request, 0, sizeof(request));
   grpc_core::ExecCtx exec_ctx;
-  grpc_closure do_nothing_closure;
+  grpc_closure destroy_after_shutdown_closure;
   grpc_auth_metadata_context null_ctx = {"", "", nullptr, nullptr};
 
   grpc_pollset* pollset =
@@ -79,8 +82,8 @@ char* grpc_test_fetch_oauth2_token_with_credentials(
   request.pops = grpc_polling_entity_create_from_pollset(pollset);
   request.is_done = false;
 
-  GRPC_CLOSURE_INIT(&do_nothing_closure, do_nothing, nullptr,
-                    grpc_schedule_on_exec_ctx);
+  GRPC_CLOSURE_INIT(&destroy_after_shutdown_closure, destroy_after_shutdown,
+                    pollset, grpc_schedule_on_exec_ctx);
 
   GRPC_CLOSURE_INIT(&request.closure, on_oauth2_response, &request,
                     grpc_schedule_on_exec_ctx);
@@ -107,8 +110,6 @@ char* grpc_test_fetch_oauth2_token_with_credentials(
   gpr_mu_unlock(request.mu);
 
   grpc_pollset_shutdown(grpc_polling_entity_pollset(&request.pops),
-                        &do_nothing_closure);
-
-  gpr_free(grpc_polling_entity_pollset(&request.pops));
+                        &destroy_after_shutdown_closure);
   return request.token;
 }

test/core/surface/public_headers_must_be_c89.c

@@ -171,6 +171,7 @@ int main(int argc, char **argv) {
   printf("%lx", (unsigned long) grpc_google_refresh_token_credentials_create);
   printf("%lx", (unsigned long) grpc_access_token_credentials_create);
   printf("%lx", (unsigned long) grpc_google_iam_credentials_create);
+  printf("%lx", (unsigned long) grpc_sts_credentials_create);
   printf("%lx", (unsigned long) grpc_metadata_credentials_create_from_plugin);
   printf("%lx", (unsigned long) grpc_secure_channel_create);
   printf("%lx", (unsigned long) grpc_server_credentials_release);