Merge pull request #983 from jboeuf/refresh_token_parsing

Adding refresh token credentials.

include/grpc/grpc_security.h

@@ -117,6 +117,15 @@ grpc_credentials *grpc_service_account_credentials_create(
 grpc_credentials *grpc_jwt_credentials_create(const char *json_key,
                                               gpr_timespec token_lifetime);
 
+/* Creates an Oauth2 Refresh Token crednetials object. May return NULL if the
+   input is invalid.
+   WARNING: Do NOT use this credentials to connect to a non-google service as
+   this could result in an oauth2 token leak.
+   - json_refresh_token is the JSON string containing the refresh token itself
+     along with a client_id and client_secret. */
+grpc_credentials *grpc_refresh_token_credentials_create(
+    const char *json_refresh_token);
+
 /* Creates a fake transport security credentials object for testing. */
 grpc_credentials *grpc_fake_transport_security_credentials_create(void);
 

src/core/security/credentials.c

@@ -46,20 +46,6 @@
 #include <grpc/support/sync.h>
 #include <grpc/support/time.h>
 
-/* -- Constants. -- */
-
-#define GRPC_SECURE_TOKEN_REFRESH_THRESHOLD_SECS 60
-
-#define GRPC_COMPUTE_ENGINE_METADATA_HOST "metadata"
-#define GRPC_COMPUTE_ENGINE_METADATA_TOKEN_PATH \
-  "/computeMetadata/v1/instance/service-accounts/default/token"
-
-#define GRPC_SERVICE_ACCOUNT_HOST "www.googleapis.com"
-#define GRPC_SERVICE_ACCOUNT_TOKEN_PATH "/oauth2/v3/token"
-#define GRPC_SERVICE_ACCOUNT_POST_BODY_PREFIX                         \
-  "grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&" \
-  "assertion="
-
 /* -- Common. -- */
 
 typedef struct {
@@ -671,8 +657,8 @@ static void service_account_fetch_oauth2(
   }
   gpr_asprintf(&body, "%s%s", GRPC_SERVICE_ACCOUNT_POST_BODY_PREFIX, jwt);
   memset(&request, 0, sizeof(grpc_httpcli_request));
-  request.host = GRPC_SERVICE_ACCOUNT_HOST;
-  request.path = GRPC_SERVICE_ACCOUNT_TOKEN_PATH;
+  request.host = GRPC_GOOGLE_OAUTH2_SERVICE_HOST;
+  request.path = GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH;
   request.hdr_count = 1;
   request.hdrs = &header;
   request.use_ssl = 1;
@@ -703,6 +689,67 @@ grpc_credentials *grpc_service_account_credentials_create(
   return &c->base.base;
 }
 
+/* -- RefreshToken credentials. -- */
+
+typedef struct {
+  grpc_oauth2_token_fetcher_credentials base;
+  grpc_auth_refresh_token refresh_token;
+} grpc_refresh_token_credentials;
+
+static void refresh_token_destroy(grpc_credentials *creds) {
+  grpc_refresh_token_credentials *c =
+      (grpc_refresh_token_credentials *)creds;
+  grpc_auth_refresh_token_destruct(&c->refresh_token);
+  oauth2_token_fetcher_destroy(&c->base.base);
+}
+
+static grpc_credentials_vtable refresh_token_vtable = {
+    refresh_token_destroy, oauth2_token_fetcher_has_request_metadata,
+    oauth2_token_fetcher_has_request_metadata_only,
+    oauth2_token_fetcher_get_request_metadata};
+
+static void refresh_token_fetch_oauth2(
+    grpc_credentials_metadata_request *metadata_req,
+    grpc_httpcli_response_cb response_cb, gpr_timespec deadline) {
+  grpc_refresh_token_credentials *c =
+      (grpc_refresh_token_credentials *)metadata_req->creds;
+  grpc_httpcli_header header = {"Content-Type",
+                                "application/x-www-form-urlencoded"};
+  grpc_httpcli_request request;
+  char *body = NULL;
+  gpr_asprintf(&body, GRPC_REFRESH_TOKEN_POST_BODY_FORMAT_STRING,
+               c->refresh_token.client_id, c->refresh_token.client_secret,
+               c->refresh_token.refresh_token);
+  memset(&request, 0, sizeof(grpc_httpcli_request));
+  request.host = GRPC_GOOGLE_OAUTH2_SERVICE_HOST;
+  request.path = GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH;
+  request.hdr_count = 1;
+  request.hdrs = &header;
+  request.use_ssl = 1;
+  grpc_httpcli_post(&request, body, strlen(body), deadline, response_cb,
+                    metadata_req);
+  gpr_free(body);
+}
+
+grpc_credentials *grpc_refresh_token_credentials_create(
+    const char *json_refresh_token) {
+  grpc_refresh_token_credentials *c;
+  grpc_auth_refresh_token refresh_token =
+      grpc_auth_refresh_token_create_from_string(json_refresh_token);
+
+  if (!grpc_auth_refresh_token_is_valid(&refresh_token)) {
+    gpr_log(GPR_ERROR,
+            "Invalid input for refresh token credentials creation");
+    return NULL;
+  }
+  c = gpr_malloc(sizeof(grpc_refresh_token_credentials));
+  memset(c, 0, sizeof(grpc_refresh_token_credentials));
+  init_oauth2_token_fetcher(&c->base, refresh_token_fetch_oauth2);
+  c->base.base.vtable = &refresh_token_vtable;
+  c->refresh_token = refresh_token;
+  return &c->base.base;
+}
+
 /* -- Fake Oauth2 credentials. -- */
 
 typedef struct {

src/core/security/credentials.h

@@ -64,6 +64,22 @@ typedef enum {
 #define GRPC_GOOGLE_WELL_KNOWN_CREDENTIALS_FILE \
   "application_default_credentials.json"
 
+#define GRPC_SECURE_TOKEN_REFRESH_THRESHOLD_SECS 60
+
+#define GRPC_COMPUTE_ENGINE_METADATA_HOST "metadata"
+#define GRPC_COMPUTE_ENGINE_METADATA_TOKEN_PATH \
+  "/computeMetadata/v1/instance/service-accounts/default/token"
+
+#define GRPC_GOOGLE_OAUTH2_SERVICE_HOST "www.googleapis.com"
+#define GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH "/oauth2/v3/token"
+
+#define GRPC_SERVICE_ACCOUNT_POST_BODY_PREFIX                         \
+  "grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&" \
+  "assertion="
+
+#define GRPC_REFRESH_TOKEN_POST_BODY_FORMAT_STRING \
+  "client_id=%s&client_secret=%s&refresh_token=%s&grant_type=refresh_token"
+
 /* --- grpc_credentials. --- */
 
 /* It is the caller's responsibility to gpr_free the result if not NULL. */

src/core/security/google_default_credentials.c

@@ -138,6 +138,23 @@ static grpc_credentials *create_jwt_creds_from_path(char *creds_path) {
   return result;
 }
 
+/* Takes ownership of creds_path if not NULL. */
+static grpc_credentials *create_refresh_token_creds_from_path(
+    char *creds_path) {
+  grpc_credentials *result = NULL;
+  gpr_slice creds_data;
+  int file_ok = 0;
+  if (creds_path == NULL) return NULL;
+  creds_data = gpr_load_file(creds_path, &file_ok);
+  gpr_free(creds_path);
+  if (file_ok) {
+    result = grpc_refresh_token_credentials_create(
+        (const char *)GPR_SLICE_START_PTR(creds_data));
+    gpr_slice_unref(creds_data);
+  }
+  return result;
+}
+
 grpc_credentials *grpc_google_default_credentials_create(void) {
   grpc_credentials *result = NULL;
   int serving_cached_credentials = 0;
@@ -157,7 +174,7 @@ grpc_credentials *grpc_google_default_credentials_create(void) {
   if (result != NULL) goto end;
 
   /* Then the well-known file. */
-  result = create_jwt_creds_from_path(
+  result = create_refresh_token_creds_from_path(
       grpc_get_well_known_google_credentials_file_path());
   if (result != NULL) goto end;
 

src/core/security/json_token.c

@@ -52,8 +52,9 @@
 /* 1 hour max. */
 const gpr_timespec grpc_max_auth_token_lifetime = {3600, 0};
 
-#define GRPC_AUTH_JSON_KEY_TYPE_INVALID "invalid"
-#define GRPC_AUTH_JSON_KEY_TYPE_SERVICE_ACCOUNT "service_account"
+#define GRPC_AUTH_JSON_TYPE_INVALID "invalid"
+#define GRPC_AUTH_JSON_TYPE_SERVICE_ACCOUNT "service_account"
+#define GRPC_AUTH_JSON_TYPE_AUTHORIZED_USER "authorized_user"
 
 #define GRPC_JWT_RSA_SHA256_ALGORITHM "RS256"
 #define GRPC_JWT_TYPE "JWT"
@@ -87,7 +88,7 @@ static int set_json_key_string_property(grpc_json *json, const char *prop_name,
 
 int grpc_auth_json_key_is_valid(const grpc_auth_json_key *json_key) {
   return (json_key != NULL) &&
-         strcmp(json_key->type, GRPC_AUTH_JSON_KEY_TYPE_INVALID);
+         strcmp(json_key->type, GRPC_AUTH_JSON_TYPE_INVALID);
 }
 
 grpc_auth_json_key grpc_auth_json_key_create_from_string(
@@ -100,7 +101,7 @@ grpc_auth_json_key grpc_auth_json_key_create_from_string(
   int success = 0;
 
   memset(&result, 0, sizeof(grpc_auth_json_key));
-  result.type = GRPC_AUTH_JSON_KEY_TYPE_INVALID;
+  result.type = GRPC_AUTH_JSON_TYPE_INVALID;
   if (json == NULL) {
     gpr_log(GPR_ERROR, "Invalid json string %s", json_string);
     goto end;
@@ -108,10 +109,10 @@ grpc_auth_json_key grpc_auth_json_key_create_from_string(
 
   prop_value = json_get_string_property(json, "type");
   if (prop_value == NULL ||
-      strcmp(prop_value, GRPC_AUTH_JSON_KEY_TYPE_SERVICE_ACCOUNT)) {
+      strcmp(prop_value, GRPC_AUTH_JSON_TYPE_SERVICE_ACCOUNT)) {
     goto end;
   }
-  result.type = GRPC_AUTH_JSON_KEY_TYPE_SERVICE_ACCOUNT;
+  result.type = GRPC_AUTH_JSON_TYPE_SERVICE_ACCOUNT;
 
   if (!set_json_key_string_property(json, "private_key_id",
                                     &result.private_key_id) ||
@@ -148,7 +149,7 @@ end:
 
 void grpc_auth_json_key_destruct(grpc_auth_json_key *json_key) {
   if (json_key == NULL) return;
-  json_key->type = GRPC_AUTH_JSON_KEY_TYPE_INVALID;
+  json_key->type = GRPC_AUTH_JSON_TYPE_INVALID;
   if (json_key->client_id != NULL) {
     gpr_free(json_key->client_id);
     json_key->client_id = NULL;
@@ -331,3 +332,67 @@ void grpc_jwt_encode_and_sign_set_override(
     grpc_jwt_encode_and_sign_override func) {
   g_jwt_encode_and_sign_override = func;
 }
+
+/* --- grpc_auth_refresh_token --- */
+
+int grpc_auth_refresh_token_is_valid(
+    const grpc_auth_refresh_token *refresh_token) {
+  return (refresh_token != NULL) &&
+         strcmp(refresh_token->type, GRPC_AUTH_JSON_TYPE_INVALID);
+}
+
+grpc_auth_refresh_token grpc_auth_refresh_token_create_from_string(
+    const char *json_string) {
+  grpc_auth_refresh_token result;
+  char *scratchpad = gpr_strdup(json_string);
+  grpc_json *json = grpc_json_parse_string(scratchpad);
+  const char *prop_value;
+  int success = 0;
+
+  memset(&result, 0, sizeof(grpc_auth_refresh_token));
+  result.type = GRPC_AUTH_JSON_TYPE_INVALID;
+  if (json == NULL) {
+    gpr_log(GPR_ERROR, "Invalid json string %s", json_string);
+    goto end;
+  }
+
+  prop_value = json_get_string_property(json, "type");
+  if (prop_value == NULL ||
+      strcmp(prop_value, GRPC_AUTH_JSON_TYPE_AUTHORIZED_USER)) {
+    goto end;
+  }
+  result.type = GRPC_AUTH_JSON_TYPE_AUTHORIZED_USER;
+
+  if (!set_json_key_string_property(json, "client_secret",
+                                    &result.client_secret) ||
+      !set_json_key_string_property(json, "client_id", &result.client_id) ||
+      !set_json_key_string_property(json, "refresh_token",
+                                    &result.refresh_token)) {
+    goto end;
+  }
+  success = 1;
+
+end:
+  if (json != NULL) grpc_json_destroy(json);
+  if (!success) grpc_auth_refresh_token_destruct(&result);
+  gpr_free(scratchpad);
+  return result;
+}
+
+void grpc_auth_refresh_token_destruct(grpc_auth_refresh_token *refresh_token) {
+  if (refresh_token == NULL) return;
+  refresh_token->type = GRPC_AUTH_JSON_TYPE_INVALID;
+  if (refresh_token->client_id != NULL) {
+    gpr_free(refresh_token->client_id);
+    refresh_token->client_id = NULL;
+  }
+  if (refresh_token->client_secret != NULL) {
+    gpr_free(refresh_token->client_secret);
+    refresh_token->client_secret = NULL;
+  }
+  if (refresh_token->refresh_token != NULL) {
+    gpr_free(refresh_token->refresh_token);
+    refresh_token->refresh_token = NULL;
+  }
+}
+

src/core/security/json_token.h

@@ -44,7 +44,7 @@
 /* --- auth_json_key parsing. --- */
 
 typedef struct {
-  char *type;
+  const char *type;
   char *private_key_id;
   char *client_id;
   char *client_email;
@@ -79,4 +79,25 @@ typedef char *(*grpc_jwt_encode_and_sign_override)(
 void grpc_jwt_encode_and_sign_set_override(
     grpc_jwt_encode_and_sign_override func);
 
+/* --- auth_refresh_token parsing. --- */
+
+typedef struct {
+  const char *type;
+  char *client_id;
+  char *client_secret;
+  char *refresh_token;
+} grpc_auth_refresh_token;
+
+/* Returns 1 if the object is valid, 0 otherwise. */
+int grpc_auth_refresh_token_is_valid(
+    const grpc_auth_refresh_token *refresh_token);
+
+/* Creates a refresh token object from string. Returns an invalid object if a
+   parsing error has been encountered. */
+grpc_auth_refresh_token grpc_auth_refresh_token_create_from_string(
+    const char *json_string);
+
+/* Destructs the object. */
+void grpc_auth_refresh_token_destruct(grpc_auth_refresh_token *refresh_token);
+
 #endif  /* GRPC_INTERNAL_CORE_SECURITY_JSON_TOKEN_H */

test/core/security/credentials_test.c

@@ -84,6 +84,13 @@ static const char test_json_key_str_part3[] =
     "\"777-abaslkan11hlb6nmim3bpspl31ud.apps.googleusercontent."
     "com\", \"type\": \"service_account\" }";
 
+/* Test refresh token. */
+static const char test_refresh_token_str[] =
+    "{ \"client_id\": \"32555999999.apps.googleusercontent.com\","
+    "  \"client_secret\": \"EmssLNjJy1332hD4KFsecret\","
+    "  \"refresh_token\": \"1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42\","
+    "  \"type\": \"authorized_user\"}";
+
 static const char valid_oauth2_json_response[] =
     "{\"access_token\":\"ya29.AHES6ZRN3-HlhAPya30GnW_bHSb_\","
     " \"expires_in\":3599, "
@@ -97,10 +104,6 @@ static const char test_signed_jwt[] =
     "eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImY0OTRkN2M1YWU2MGRmOTcyNmM4YW"
     "U0MDcyZTViYTdmZDkwODg2YzcifQ";
 
-static const char expected_service_account_http_body_prefix[] =
-    "grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&"
-    "assertion=";
-
 static const char test_service_url[] = "https://foo.com/foo.v1";
 static const char other_test_service_url[] = "https://bar.com/bar.v1";
 
@@ -463,6 +466,87 @@ static void test_compute_engine_creds_failure(void) {
   grpc_httpcli_set_override(NULL, NULL);
 }
 
+static void validate_refresh_token_http_request(
+    const grpc_httpcli_request *request, const char *body, size_t body_size) {
+  /* The content of the assertion is tested extensively in json_token_test. */
+  char *expected_body = NULL;
+  GPR_ASSERT(body != NULL);
+  GPR_ASSERT(body_size != 0);
+  gpr_asprintf(&expected_body, GRPC_REFRESH_TOKEN_POST_BODY_FORMAT_STRING,
+               "32555999999.apps.googleusercontent.com",
+               "EmssLNjJy1332hD4KFsecret",
+               "1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42");
+  GPR_ASSERT(strlen(expected_body) == body_size);
+  GPR_ASSERT(memcmp(expected_body, body, body_size) == 0);
+  gpr_free(expected_body);
+  GPR_ASSERT(request->use_ssl);
+  GPR_ASSERT(strcmp(request->host, GRPC_GOOGLE_OAUTH2_SERVICE_HOST) == 0);
+  GPR_ASSERT(strcmp(request->path, GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH) == 0);
+  GPR_ASSERT(request->hdr_count == 1);
+  GPR_ASSERT(strcmp(request->hdrs[0].key, "Content-Type") == 0);
+  GPR_ASSERT(strcmp(request->hdrs[0].value,
+                    "application/x-www-form-urlencoded") == 0);
+}
+
+static int refresh_token_httpcli_post_success(
+    const grpc_httpcli_request *request, const char *body, size_t body_size,
+    gpr_timespec deadline, grpc_httpcli_response_cb on_response,
+    void *user_data) {
+  grpc_httpcli_response response =
+      http_response(200, valid_oauth2_json_response);
+  validate_refresh_token_http_request(request, body, body_size);
+  on_response(user_data, &response);
+  return 1;
+}
+
+static int refresh_token_httpcli_post_failure(
+    const grpc_httpcli_request *request, const char *body, size_t body_size,
+    gpr_timespec deadline, grpc_httpcli_response_cb on_response,
+    void *user_data) {
+  grpc_httpcli_response response = http_response(403, "Not Authorized.");
+  validate_refresh_token_http_request(request, body, body_size);
+  on_response(user_data, &response);
+  return 1;
+}
+
+static void test_refresh_token_creds_success(void) {
+  grpc_credentials *refresh_token_creds =
+      grpc_refresh_token_credentials_create(test_refresh_token_str);
+  GPR_ASSERT(grpc_credentials_has_request_metadata(refresh_token_creds));
+  GPR_ASSERT(grpc_credentials_has_request_metadata_only(refresh_token_creds));
+
+  /* First request: http get should be called. */
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            refresh_token_httpcli_post_success);
+  grpc_credentials_get_request_metadata(refresh_token_creds, test_service_url,
+                                        on_oauth2_creds_get_metadata_success,
+                                        (void *)test_user_data);
+
+  /* Second request: the cached token should be served directly. */
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            httpcli_post_should_not_be_called);
+  grpc_credentials_get_request_metadata(refresh_token_creds, test_service_url,
+                                        on_oauth2_creds_get_metadata_success,
+                                        (void *)test_user_data);
+
+  grpc_credentials_unref(refresh_token_creds);
+  grpc_httpcli_set_override(NULL, NULL);
+}
+
+static void test_refresh_token_creds_failure(void) {
+  grpc_credentials *refresh_token_creds =
+      grpc_refresh_token_credentials_create(test_refresh_token_str);
+  grpc_httpcli_set_override(httpcli_get_should_not_be_called,
+                            refresh_token_httpcli_post_failure);
+  GPR_ASSERT(grpc_credentials_has_request_metadata(refresh_token_creds));
+  GPR_ASSERT(grpc_credentials_has_request_metadata_only(refresh_token_creds));
+  grpc_credentials_get_request_metadata(refresh_token_creds, test_service_url,
+                                        on_oauth2_creds_get_metadata_failure,
+                                        (void *)test_user_data);
+  grpc_credentials_unref(refresh_token_creds);
+  grpc_httpcli_set_override(NULL, NULL);
+}
+
 static void validate_jwt_encode_and_sign_params(
     const grpc_auth_json_key *json_key, const char *scope,
     gpr_timespec token_lifetime) {
@@ -515,13 +599,13 @@ static void validate_service_account_http_request(
   GPR_ASSERT(body != NULL);
   GPR_ASSERT(body_size != 0);
   gpr_asprintf(&expected_body, "%s%s",
-               expected_service_account_http_body_prefix, test_signed_jwt);
+               GRPC_SERVICE_ACCOUNT_POST_BODY_PREFIX, test_signed_jwt);
   GPR_ASSERT(strlen(expected_body) == body_size);
-  GPR_ASSERT(!memcmp(expected_body, body, body_size));
+  GPR_ASSERT(memcmp(expected_body, body, body_size) == 0);
   gpr_free(expected_body);
   GPR_ASSERT(request->use_ssl);
-  GPR_ASSERT(strcmp(request->host, "www.googleapis.com") == 0);
-  GPR_ASSERT(strcmp(request->path, "/oauth2/v3/token") == 0);
+  GPR_ASSERT(strcmp(request->host, GRPC_GOOGLE_OAUTH2_SERVICE_HOST) == 0);
+  GPR_ASSERT(strcmp(request->path, GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH) == 0);
   GPR_ASSERT(request->hdr_count == 1);
   GPR_ASSERT(strcmp(request->hdrs[0].key, "Content-Type") == 0);
   GPR_ASSERT(strcmp(request->hdrs[0].value,
@@ -711,6 +795,8 @@ int main(int argc, char **argv) {
   test_ssl_oauth2_iam_composite_creds();
   test_compute_engine_creds_success();
   test_compute_engine_creds_failure();
+  test_refresh_token_creds_success();
+  test_refresh_token_creds_failure();
   test_service_account_creds_success();
   test_service_account_creds_http_failure();
   test_service_account_creds_signing_failure();

test/core/security/fetch_oauth2.c

@@ -34,7 +34,6 @@
 #include <stdio.h>
 #include <string.h>
 
-#include "src/core/security/credentials.h"
 #include <grpc/grpc.h>
 #include <grpc/grpc_security.h>
 #include <grpc/support/alloc.h>
@@ -43,6 +42,9 @@
 #include <grpc/support/slice.h>
 #include <grpc/support/sync.h>
 
+#include "src/core/security/credentials.h"
+#include "src/core/support/file.h"
+
 typedef struct {
   gpr_cv cv;
   gpr_mu mu;
@@ -74,50 +76,50 @@ static void on_oauth2_response(void *user_data, grpc_mdelem **md_elems,
 
 static grpc_credentials *create_service_account_creds(
     const char *json_key_file_path, const char *scope) {
-  char json_key[8192]; /* Should be plenty. */
-  char *current = json_key;
-  FILE *json_key_file = fopen(json_key_file_path, "r");
-  if (json_key_file == NULL) {
-    gpr_log(GPR_ERROR, "Invalid path for json key file: %s.",
-            json_key_file_path);
+  int success;
+  gpr_slice json_key = gpr_load_file(json_key_file_path, &success);
+  if (!success) {
+    gpr_log(GPR_ERROR, "Could not read file %s.", json_key_file_path);
     exit(1);
   }
+  return grpc_service_account_credentials_create(
+      (const char *)GPR_SLICE_START_PTR(json_key), scope,
+      grpc_max_auth_token_lifetime);
+}
 
-  do {
-    size_t bytes_read = fread(
-        current, 1, sizeof(json_key) - (current - json_key), json_key_file);
-    if (bytes_read == 0) {
-      if (!feof(json_key_file)) {
-        gpr_log(GPR_ERROR, "Error occured while reading %s.",
-                json_key_file_path);
-        exit(1);
-      }
-      break;
-    }
-    current += bytes_read;
-  } while (sizeof(json_key) > (size_t)(current - json_key));
-
-  if ((current - json_key) == sizeof(json_key)) {
-    gpr_log(GPR_ERROR, "Json key file %s exceeds size limit (%d bytes).",
-            json_key_file_path, (int)sizeof(json_key));
+static grpc_credentials *create_refresh_token_creds(
+    const char *json_refresh_token_file_path) {
+  int success;
+  gpr_slice refresh_token =
+      gpr_load_file(json_refresh_token_file_path, &success);
+  if (!success) {
+    gpr_log(GPR_ERROR, "Could not read file %s.", json_refresh_token_file_path);
     exit(1);
   }
-  fclose(json_key_file);
-
-  return grpc_service_account_credentials_create(json_key, scope,
-                                                 grpc_max_auth_token_lifetime);
+  return grpc_refresh_token_credentials_create(
+      (const char *)GPR_SLICE_START_PTR(refresh_token));
 }
 
 int main(int argc, char **argv) {
   synchronizer sync;
   grpc_credentials *creds = NULL;
   char *json_key_file_path = NULL;
+  char *json_refresh_token_file_path = NULL;
   int use_gce = 0;
   char *scope = NULL;
   gpr_cmdline *cl = gpr_cmdline_create("fetch_oauth2");
-  gpr_cmdline_add_string(cl, "json_key", "File path of the json key.",
+  gpr_cmdline_add_string(cl, "json_key",
+                         "File path of the json key. Mutually exclusive with "
+                         "--json_refresh_token.",
                          &json_key_file_path);
-  gpr_cmdline_add_string(cl, "scope", "Space delimited permissions.", &scope);
+  gpr_cmdline_add_string(cl, "json_refresh_token",
+                         "File path of the json refresh token. Mutually "
+                         "exclusive with --json_key.",
+                         &json_refresh_token_file_path);
+  gpr_cmdline_add_string(cl, "scope",
+                         "Space delimited permissions. Only used for "
+                         "--json_key, ignored otherwise.",
+                         &scope);
   gpr_cmdline_add_flag(
       cl, "gce",
       "Get a token from the GCE metadata server (only works in GCE).",
@@ -126,6 +128,12 @@ int main(int argc, char **argv) {
 
   grpc_init();
 
+  if (json_key_file_path != NULL && json_refresh_token_file_path != NULL) {
+    gpr_log(GPR_ERROR,
+            "--json_key and --json_refresh_token are mutually exclusive.");
+    exit(1);
+  }
+
   if (use_gce) {
     if (json_key_file_path != NULL || scope != NULL) {
       gpr_log(GPR_INFO,
@@ -137,6 +145,15 @@ int main(int argc, char **argv) {
       gpr_log(GPR_ERROR, "Could not create gce credentials.");
       exit(1);
     }
+  } else if (json_refresh_token_file_path != NULL) {
+    creds = create_refresh_token_creds(json_refresh_token_file_path);
+    if (creds == NULL) {
+      gpr_log(GPR_ERROR,
+              "Could not create refresh token creds. %s does probably not "
+              "contain a valid json refresh token.",
+              json_refresh_token_file_path);
+      exit(1);
+    }
   } else {
     if (json_key_file_path == NULL) {
       gpr_log(GPR_ERROR, "Missing --json_key option.");

test/core/security/json_token_test.c

@@ -78,6 +78,13 @@ static const char test_json_key_str_part3[] =
     "\"777-abaslkan11hlb6nmim3bpspl31ud.apps.googleusercontent."
     "com\", \"type\": \"service_account\" }";
 
+/* Test refresh token. */
+static const char test_refresh_token_str[] =
+    "{ \"client_id\": \"32555999999.apps.googleusercontent.com\","
+    "  \"client_secret\": \"EmssLNjJy1332hD4KFsecret\","
+    "  \"refresh_token\": \"1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42\","
+    "  \"type\": \"authorized_user\"}";
+
 static const char test_scope[] = "myperm1 myperm2";
 
 static const char test_service_url[] = "https://foo.com/foo.v1";
@@ -419,6 +426,64 @@ static void test_jwt_creds_jwt_encode_and_sign(void) {
                            jwt_creds_check_jwt_claim);
 }
 
+static void test_parse_refresh_token_success(void) {
+  grpc_auth_refresh_token refresh_token =
+      grpc_auth_refresh_token_create_from_string(test_refresh_token_str);
+  GPR_ASSERT(grpc_auth_refresh_token_is_valid(&refresh_token));
+  GPR_ASSERT(refresh_token.type != NULL &&
+             (strcmp(refresh_token.type, "authorized_user") == 0));
+  GPR_ASSERT(refresh_token.client_id != NULL &&
+             (strcmp(refresh_token.client_id,
+                     "32555999999.apps.googleusercontent.com") == 0));
+  GPR_ASSERT(
+      refresh_token.client_secret != NULL &&
+      (strcmp(refresh_token.client_secret, "EmssLNjJy1332hD4KFsecret") == 0));
+  GPR_ASSERT(refresh_token.refresh_token != NULL &&
+             (strcmp(refresh_token.refresh_token,
+                     "1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42") == 0));
+  grpc_auth_refresh_token_destruct(&refresh_token);
+}
+
+static void test_parse_refresh_token_failure_no_type(void) {
+  const char refresh_token_str[] =
+      "{ \"client_id\": \"32555999999.apps.googleusercontent.com\","
+      "  \"client_secret\": \"EmssLNjJy1332hD4KFsecret\","
+      "  \"refresh_token\": \"1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42\"}";
+  grpc_auth_refresh_token refresh_token =
+      grpc_auth_refresh_token_create_from_string(refresh_token_str);
+  GPR_ASSERT(!grpc_auth_refresh_token_is_valid(&refresh_token));
+}
+
+static void test_parse_refresh_token_failure_no_client_id(void) {
+  const char refresh_token_str[] =
+      "{ \"client_secret\": \"EmssLNjJy1332hD4KFsecret\","
+      "  \"refresh_token\": \"1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42\","
+      "  \"type\": \"authorized_user\"}";
+  grpc_auth_refresh_token refresh_token =
+      grpc_auth_refresh_token_create_from_string(refresh_token_str);
+  GPR_ASSERT(!grpc_auth_refresh_token_is_valid(&refresh_token));
+}
+
+static void test_parse_refresh_token_failure_no_client_secret(void) {
+  const char refresh_token_str[] =
+      "{ \"client_id\": \"32555999999.apps.googleusercontent.com\","
+      "  \"refresh_token\": \"1/Blahblasj424jladJDSGNf-u4Sua3HDA2ngjd42\","
+      "  \"type\": \"authorized_user\"}";
+  grpc_auth_refresh_token refresh_token =
+      grpc_auth_refresh_token_create_from_string(refresh_token_str);
+  GPR_ASSERT(!grpc_auth_refresh_token_is_valid(&refresh_token));
+}
+
+static void test_parse_refresh_token_failure_no_refresh_token(void) {
+  const char refresh_token_str[] =
+      "{ \"client_id\": \"32555999999.apps.googleusercontent.com\","
+      "  \"client_secret\": \"EmssLNjJy1332hD4KFsecret\","
+      "  \"type\": \"authorized_user\"}";
+  grpc_auth_refresh_token refresh_token =
+      grpc_auth_refresh_token_create_from_string(refresh_token_str);
+  GPR_ASSERT(!grpc_auth_refresh_token_is_valid(&refresh_token));
+}
+
 int main(int argc, char **argv) {
   grpc_test_init(argc, argv);
   test_parse_json_key_success();
@@ -430,5 +495,10 @@ int main(int argc, char **argv) {
   test_parse_json_key_failure_no_private_key();
   test_service_account_creds_jwt_encode_and_sign();
   test_jwt_creds_jwt_encode_and_sign();
+  test_parse_refresh_token_success();
+  test_parse_refresh_token_failure_no_type();
+  test_parse_refresh_token_failure_no_client_id();
+  test_parse_refresh_token_failure_no_client_secret();
+  test_parse_refresh_token_failure_no_refresh_token();
   return 0;
 }