Merge pull request #4154 from jboeuf/new_creds_plugin_api

Changing the credentials plugin API.

include/grpc/grpc_security.h

@@ -41,6 +41,81 @@
 extern "C" {
 #endif
 
+/* --- Authentication Context. --- */
+
+#define GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME "transport_security_type"
+#define GRPC_SSL_TRANSPORT_SECURITY_TYPE "ssl"
+
+#define GRPC_X509_CN_PROPERTY_NAME "x509_common_name"
+#define GRPC_X509_SAN_PROPERTY_NAME "x509_subject_alternative_name"
+
+typedef struct grpc_auth_context grpc_auth_context;
+
+typedef struct grpc_auth_property_iterator {
+  const grpc_auth_context *ctx;
+  size_t index;
+  const char *name;
+} grpc_auth_property_iterator;
+
+/* value, if not NULL, is guaranteed to be NULL terminated. */
+typedef struct grpc_auth_property {
+  char *name;
+  char *value;
+  size_t value_length;
+} grpc_auth_property;
+
+/* Returns NULL when the iterator is at the end. */
+const grpc_auth_property *grpc_auth_property_iterator_next(
+    grpc_auth_property_iterator *it);
+
+/* Iterates over the auth context. */
+grpc_auth_property_iterator grpc_auth_context_property_iterator(
+    const grpc_auth_context *ctx);
+
+/* Gets the peer identity. Returns an empty iterator (first _next will return
+   NULL) if the peer is not authenticated. */
+grpc_auth_property_iterator grpc_auth_context_peer_identity(
+    const grpc_auth_context *ctx);
+
+/* Finds a property in the context. May return an empty iterator (first _next
+   will return NULL) if no property with this name was found in the context. */
+grpc_auth_property_iterator grpc_auth_context_find_properties_by_name(
+    const grpc_auth_context *ctx, const char *name);
+
+/* Gets the name of the property that indicates the peer identity. Will return
+   NULL if the peer is not authenticated. */
+const char *grpc_auth_context_peer_identity_property_name(
+    const grpc_auth_context *ctx);
+
+/* Returns 1 if the peer is authenticated, 0 otherwise. */
+int grpc_auth_context_peer_is_authenticated(const grpc_auth_context *ctx);
+
+/* Gets the auth context from the call. Caller needs to call
+   grpc_auth_context_release on the returned context. */
+grpc_auth_context *grpc_call_auth_context(grpc_call *call);
+
+/* Releases the auth context returned from grpc_call_auth_context. */
+void grpc_auth_context_release(grpc_auth_context *context);
+
+/* --
+   The following auth context methods should only be called by a server metadata
+   processor to set properties extracted from auth metadata.
+   -- */
+
+/* Add a property. */
+void grpc_auth_context_add_property(grpc_auth_context *ctx, const char *name,
+                                    const char *value, size_t value_length);
+
+/* Add a C string property. */
+void grpc_auth_context_add_cstring_property(grpc_auth_context *ctx,
+                                            const char *name,
+                                            const char *value);
+
+/* Sets the property name. Returns 1 if successful or 0 in case of failure
+   (which means that no property with this name exists). */
+int grpc_auth_context_set_peer_identity_property_name(grpc_auth_context *ctx,
+                                                      const char *name);
+
 /* --- grpc_channel_credentials object. ---
 
    A channel credentials object represents a way to authenticate a client on a
@@ -165,6 +240,24 @@ typedef void (*grpc_credentials_plugin_metadata_cb)(
     void *user_data, const grpc_metadata *creds_md, size_t num_creds_md,
     grpc_status_code status, const char *error_details);
 
+/* Context that can be used by metadata credentials plugin in order to create
+   auth related metadata. */
+typedef struct {
+  /* The fully qualifed service url. */
+  const char *service_url;
+
+  /* The method name of the RPC being called (not fully qualified).
+     The fully qualified method name can be built from the service_url:
+     full_qualified_method_name = ctx->service_url + '/' + ctx->method_name. */
+  const char *method_name;
+
+  /* The auth_context of the channel which gives the server's identity. */
+  const grpc_auth_context *channel_auth_context;
+
+  /* Reserved for future use. */
+  void *reserved;
+} grpc_auth_metadata_context;
+
 /* grpc_metadata_credentials plugin is an API user provided structure used to
    create grpc_credentials objects that can be set on a channel (composed) or
    a call. See grpc_credentials_metadata_create_from_plugin below.
@@ -172,11 +265,11 @@ typedef void (*grpc_credentials_plugin_metadata_cb)(
    every call in scope for the credentials created from it. */
 typedef struct {
   /* The implementation of this method has to be non-blocking.
-     - service_url is the fully qualified URL that the client stack is
-       connecting to.
+     - context is the information that can be used by the plugin to create auth
+       metadata.
      - cb is the callback that needs to be called when the metadata is ready.
      - user_data needs to be passed as the first parameter of the callback. */
-  void (*get_metadata)(void *state, const char *service_url,
+  void (*get_metadata)(void *state, grpc_auth_metadata_context context,
                        grpc_credentials_plugin_metadata_cb cb, void *user_data);
 
   /* Destroys the plugin state. */
@@ -184,6 +277,9 @@ typedef struct {
 
   /* State that will be set as the first parameter of the methods above. */
   void *state;
+
+  /* Type of credentials that this plugin is implementing. */
+  const char *type;
 } grpc_metadata_credentials_plugin;
 
 /* Creates a credentials object from a plugin. */
@@ -239,81 +335,6 @@ int grpc_server_add_secure_http2_port(grpc_server *server, const char *addr,
 grpc_call_error grpc_call_set_credentials(grpc_call *call,
                                           grpc_call_credentials *creds);
 
-/* --- Authentication Context. --- */
-
-#define GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME "transport_security_type"
-#define GRPC_SSL_TRANSPORT_SECURITY_TYPE "ssl"
-
-#define GRPC_X509_CN_PROPERTY_NAME "x509_common_name"
-#define GRPC_X509_SAN_PROPERTY_NAME "x509_subject_alternative_name"
-
-typedef struct grpc_auth_context grpc_auth_context;
-
-typedef struct grpc_auth_property_iterator {
-  const grpc_auth_context *ctx;
-  size_t index;
-  const char *name;
-} grpc_auth_property_iterator;
-
-/* value, if not NULL, is guaranteed to be NULL terminated. */
-typedef struct grpc_auth_property {
-  char *name;
-  char *value;
-  size_t value_length;
-} grpc_auth_property;
-
-/* Returns NULL when the iterator is at the end. */
-const grpc_auth_property *grpc_auth_property_iterator_next(
-    grpc_auth_property_iterator *it);
-
-/* Iterates over the auth context. */
-grpc_auth_property_iterator grpc_auth_context_property_iterator(
-    const grpc_auth_context *ctx);
-
-/* Gets the peer identity. Returns an empty iterator (first _next will return
-   NULL) if the peer is not authenticated. */
-grpc_auth_property_iterator grpc_auth_context_peer_identity(
-    const grpc_auth_context *ctx);
-
-/* Finds a property in the context. May return an empty iterator (first _next
-   will return NULL) if no property with this name was found in the context. */
-grpc_auth_property_iterator grpc_auth_context_find_properties_by_name(
-    const grpc_auth_context *ctx, const char *name);
-
-/* Gets the name of the property that indicates the peer identity. Will return
-   NULL if the peer is not authenticated. */
-const char *grpc_auth_context_peer_identity_property_name(
-    const grpc_auth_context *ctx);
-
-/* Returns 1 if the peer is authenticated, 0 otherwise. */
-int grpc_auth_context_peer_is_authenticated(const grpc_auth_context *ctx);
-
-/* Gets the auth context from the call. Caller needs to call
-   grpc_auth_context_release on the returned context. */
-grpc_auth_context *grpc_call_auth_context(grpc_call *call);
-
-/* Releases the auth context returned from grpc_call_auth_context. */
-void grpc_auth_context_release(grpc_auth_context *context);
-
-/* --
-   The following auth context methods should only be called by a server metadata
-   processor to set properties extracted from auth metadata.
-   -- */
-
-/* Add a property. */
-void grpc_auth_context_add_property(grpc_auth_context *ctx, const char *name,
-                                    const char *value, size_t value_length);
-
-/* Add a C string property. */
-void grpc_auth_context_add_cstring_property(grpc_auth_context *ctx,
-                                            const char *name,
-                                            const char *value);
-
-/* Sets the property name. Returns 1 if successful or 0 in case of failure
-   (which means that no property with this name exists). */
-int grpc_auth_context_set_peer_identity_property_name(grpc_auth_context *ctx,
-                                                      const char *name);
-
 /* --- Auth Metadata Processing --- */
 
 /* Callback function that is called when the metadata processing is done.

src/core/security/client_auth_filter.c

@@ -63,7 +63,7 @@ typedef struct {
   int sent_initial_metadata;
   gpr_uint8 security_context_set;
   grpc_linked_mdelem md_links[MAX_CREDENTIALS_METADATA_COUNT];
-  char *service_url;
+  grpc_auth_metadata_context auth_md_context;
 } call_data;
 
 /* We can have a per-channel credentials. */
@@ -76,11 +76,20 @@ typedef struct {
   grpc_mdstr *status_key;
 } channel_data;
 
-static void reset_service_url(call_data *calld) {
-  if (calld->service_url != NULL) {
-    gpr_free(calld->service_url);
-    calld->service_url = NULL;
+static void reset_auth_metadata_context(
+    grpc_auth_metadata_context *auth_md_context) {
+  if (auth_md_context->service_url != NULL) {
+    gpr_free((char *)auth_md_context->service_url);
+    auth_md_context->service_url = NULL;
   }
+  if (auth_md_context->method_name != NULL) {
+    gpr_free((char *)auth_md_context->method_name);
+    auth_md_context->method_name = NULL;
+  }
+  GRPC_AUTH_CONTEXT_UNREF(
+      (grpc_auth_context *)auth_md_context->channel_auth_context,
+      "grpc_auth_metadata_context");
+  auth_md_context->channel_auth_context = NULL;
 }
 
 static void bubble_up_error(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
@@ -101,7 +110,7 @@ static void on_credentials_metadata(grpc_exec_ctx *exec_ctx, void *user_data,
   grpc_transport_stream_op *op = &calld->op;
   grpc_metadata_batch *mdb;
   size_t i;
-  reset_service_url(calld);
+  reset_auth_metadata_context(&calld->auth_md_context);
   if (status != GRPC_CREDENTIALS_OK) {
     bubble_up_error(exec_ctx, elem, GRPC_STATUS_UNAUTHENTICATED,
                     "Credentials failed to get metadata.");
@@ -120,9 +129,13 @@ static void on_credentials_metadata(grpc_exec_ctx *exec_ctx, void *user_data,
   grpc_call_next_op(exec_ctx, elem, op);
 }
 
-void build_service_url(const char *url_scheme, call_data *calld) {
+void build_auth_metadata_context(grpc_security_connector *sc,
+                                 call_data *calld) {
   char *service = gpr_strdup(grpc_mdstr_as_c_string(calld->method));
   char *last_slash = strrchr(service, '/');
+  char *method_name = NULL;
+  char *service_url = NULL;
+  reset_auth_metadata_context(&calld->auth_md_context);
   if (last_slash == NULL) {
     gpr_log(GPR_ERROR, "No '/' found in fully qualified method name");
     service[0] = '\0';
@@ -131,11 +144,16 @@ void build_service_url(const char *url_scheme, call_data *calld) {
     service[1] = '\0';
   } else {
     *last_slash = '\0';
+    method_name = gpr_strdup(last_slash + 1);
   }
-  if (url_scheme == NULL) url_scheme = "";
-  reset_service_url(calld);
-  gpr_asprintf(&calld->service_url, "%s://%s%s", url_scheme,
+  if (method_name == NULL) method_name = gpr_strdup("");
+  gpr_asprintf(&service_url, "%s://%s%s",
+               sc->url_scheme == NULL ? "" : sc->url_scheme,
                grpc_mdstr_as_c_string(calld->host), service);
+  calld->auth_md_context.service_url = service_url;
+  calld->auth_md_context.method_name = method_name;
+  calld->auth_md_context.channel_auth_context = GRPC_AUTH_CONTEXT_REF(
+      sc->auth_context, "grpc_auth_metadata_context");
   gpr_free(service);
 }
 
@@ -169,12 +187,12 @@ static void send_security_metadata(grpc_exec_ctx *exec_ctx,
         call_creds_has_md ? ctx->creds : channel_call_creds);
   }
 
-  build_service_url(chand->security_connector->base.url_scheme, calld);
+  build_auth_metadata_context(&chand->security_connector->base, calld);
   calld->op = *op; /* Copy op (originates from the caller's stack). */
   GPR_ASSERT(calld->pollset);
-  grpc_call_credentials_get_request_metadata(exec_ctx, calld->creds,
-                                             calld->pollset, calld->service_url,
-                                             on_credentials_metadata, elem);
+  grpc_call_credentials_get_request_metadata(
+      exec_ctx, calld->creds, calld->pollset, calld->auth_md_context,
+      on_credentials_metadata, elem);
 }
 
 static void on_host_checked(grpc_exec_ctx *exec_ctx, void *user_data,
@@ -297,7 +315,7 @@ static void destroy_call_elem(grpc_exec_ctx *exec_ctx,
   if (calld->method != NULL) {
     GRPC_MDSTR_UNREF(calld->method);
   }
-  reset_service_url(calld);
+  reset_auth_metadata_context(&calld->auth_md_context);
 }
 
 /* Constructor for channel_data */

src/core/security/credentials.c

@@ -33,16 +33,16 @@
 
 #include "src/core/security/credentials.h"
 
-#include <string.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "src/core/channel/channel_args.h"
 #include "src/core/channel/http_client_filter.h"
-#include "src/core/json/json.h"
 #include "src/core/httpcli/httpcli.h"
 #include "src/core/iomgr/iomgr.h"
-#include "src/core/surface/api_trace.h"
+#include "src/core/json/json.h"
 #include "src/core/support/string.h"
+#include "src/core/surface/api_trace.h"
 
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
@@ -117,15 +117,16 @@ void grpc_call_credentials_release(grpc_call_credentials *creds) {
 }
 
 void grpc_call_credentials_get_request_metadata(
-    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds, grpc_pollset *pollset,
-    const char *service_url, grpc_credentials_metadata_cb cb, void *user_data) {
+    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds,
+    grpc_pollset *pollset, grpc_auth_metadata_context context,
+    grpc_credentials_metadata_cb cb, void *user_data) {
   if (creds == NULL || creds->vtable->get_request_metadata == NULL) {
     if (cb != NULL) {
       cb(exec_ctx, user_data, NULL, 0, GRPC_CREDENTIALS_OK);
     }
     return;
   }
-  creds->vtable->get_request_metadata(exec_ctx, creds, pollset, service_url, cb,
+  creds->vtable->get_request_metadata(exec_ctx, creds, pollset, context, cb,
                                       user_data);
 }
 
@@ -207,8 +208,7 @@ grpc_arg grpc_server_credentials_to_arg(grpc_server_credentials *p) {
   return arg;
 }
 
-grpc_server_credentials *grpc_server_credentials_from_arg(
-    const grpc_arg *arg) {
+grpc_server_credentials *grpc_server_credentials_from_arg(const grpc_arg *arg) {
   if (strcmp(arg->key, GRPC_SERVER_CREDENTIALS_ARG) != 0) return NULL;
   if (arg->type != GRPC_ARG_POINTER) {
     gpr_log(GPR_ERROR, "Invalid type %d for arg %s", arg->type,
@@ -424,9 +424,12 @@ static void jwt_destruct(grpc_call_credentials *creds) {
   gpr_mu_destroy(&c->cache_mu);
 }
 
-static void jwt_get_request_metadata(
-    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds, grpc_pollset *pollset,
-    const char *service_url, grpc_credentials_metadata_cb cb, void *user_data) {
+static void jwt_get_request_metadata(grpc_exec_ctx *exec_ctx,
+                                     grpc_call_credentials *creds,
+                                     grpc_pollset *pollset,
+                                     grpc_auth_metadata_context context,
+                                     grpc_credentials_metadata_cb cb,
+                                     void *user_data) {
   grpc_service_account_jwt_access_credentials *c =
       (grpc_service_account_jwt_access_credentials *)creds;
   gpr_timespec refresh_threshold = gpr_time_from_seconds(
@@ -437,7 +440,7 @@ static void jwt_get_request_metadata(
   {
     gpr_mu_lock(&c->cache_mu);
     if (c->cached.service_url != NULL &&
-        strcmp(c->cached.service_url, service_url) == 0 &&
+        strcmp(c->cached.service_url, context.service_url) == 0 &&
         c->cached.jwt_md != NULL &&
         (gpr_time_cmp(gpr_time_sub(c->cached.jwt_expiration,
                                    gpr_now(GPR_CLOCK_REALTIME)),
@@ -452,14 +455,15 @@ static void jwt_get_request_metadata(
     /* Generate a new jwt. */
     gpr_mu_lock(&c->cache_mu);
     jwt_reset_cache(c);
-    jwt = grpc_jwt_encode_and_sign(&c->key, service_url, c->jwt_lifetime, NULL);
+    jwt = grpc_jwt_encode_and_sign(&c->key, context.service_url,
+                                   c->jwt_lifetime, NULL);
     if (jwt != NULL) {
       char *md_value;
       gpr_asprintf(&md_value, "Bearer %s", jwt);
       gpr_free(jwt);
       c->cached.jwt_expiration =
           gpr_time_add(gpr_now(GPR_CLOCK_REALTIME), c->jwt_lifetime);
-      c->cached.service_url = gpr_strdup(service_url);
+      c->cached.service_url = gpr_strdup(context.service_url);
       c->cached.jwt_md = grpc_credentials_md_store_create(1);
       grpc_credentials_md_store_add_cstrings(
           c->cached.jwt_md, GRPC_AUTHORIZATION_METADATA_KEY, md_value);
@@ -644,7 +648,7 @@ static void on_oauth2_token_fetcher_http_response(
 
 static void oauth2_token_fetcher_get_request_metadata(
     grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds,
-    grpc_pollset *pollset, const char *service_url,
+    grpc_pollset *pollset, grpc_auth_metadata_context context,
     grpc_credentials_metadata_cb cb, void *user_data) {
   grpc_oauth2_token_fetcher_credentials *c =
       (grpc_oauth2_token_fetcher_credentials *)creds;
@@ -800,8 +804,9 @@ static void on_simulated_token_fetch_done(void *user_data) {
 }
 
 static void md_only_test_get_request_metadata(
-    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds, grpc_pollset *pollset,
-    const char *service_url, grpc_credentials_metadata_cb cb, void *user_data) {
+    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds,
+    grpc_pollset *pollset, grpc_auth_metadata_context context,
+    grpc_credentials_metadata_cb cb, void *user_data) {
   grpc_md_only_test_credentials *c = (grpc_md_only_test_credentials *)creds;
 
   if (c->is_async) {
@@ -839,8 +844,9 @@ static void access_token_destruct(grpc_call_credentials *creds) {
 }
 
 static void access_token_get_request_metadata(
-    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds, grpc_pollset *pollset,
-    const char *service_url, grpc_credentials_metadata_cb cb, void *user_data) {
+    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds,
+    grpc_pollset *pollset, grpc_auth_metadata_context context,
+    grpc_credentials_metadata_cb cb, void *user_data) {
   grpc_access_token_credentials *c = (grpc_access_token_credentials *)creds;
   cb(exec_ctx, user_data, c->access_token_md->entries, 1, GRPC_CREDENTIALS_OK);
 }
@@ -921,7 +927,7 @@ typedef struct {
   grpc_composite_call_credentials *composite_creds;
   size_t creds_index;
   grpc_credentials_md_store *md_elems;
-  char *service_url;
+  grpc_auth_metadata_context auth_md_context;
   void *user_data;
   grpc_pollset *pollset;
   grpc_credentials_metadata_cb cb;
@@ -939,7 +945,6 @@ static void composite_call_destruct(grpc_call_credentials *creds) {
 static void composite_call_md_context_destroy(
     grpc_composite_call_credentials_metadata_context *ctx) {
   grpc_credentials_md_store_unref(ctx->md_elems);
-  if (ctx->service_url != NULL) gpr_free(ctx->service_url);
   gpr_free(ctx);
 }
 
@@ -967,9 +972,9 @@ static void composite_call_metadata_cb(grpc_exec_ctx *exec_ctx, void *user_data,
   if (ctx->creds_index < ctx->composite_creds->inner.num_creds) {
     grpc_call_credentials *inner_creds =
         ctx->composite_creds->inner.creds_array[ctx->creds_index++];
-    grpc_call_credentials_get_request_metadata(exec_ctx, inner_creds,
-                                               ctx->pollset, ctx->service_url,
-                                               composite_call_metadata_cb, ctx);
+    grpc_call_credentials_get_request_metadata(
+        exec_ctx, inner_creds, ctx->pollset, ctx->auth_md_context,
+        composite_call_metadata_cb, ctx);
     return;
   }
 
@@ -980,22 +985,23 @@ static void composite_call_metadata_cb(grpc_exec_ctx *exec_ctx, void *user_data,
 }
 
 static void composite_call_get_request_metadata(
-    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds, grpc_pollset *pollset,
-    const char *service_url, grpc_credentials_metadata_cb cb, void *user_data) {
+    grpc_exec_ctx *exec_ctx, grpc_call_credentials *creds,
+    grpc_pollset *pollset, grpc_auth_metadata_context auth_md_context,
+    grpc_credentials_metadata_cb cb, void *user_data) {
   grpc_composite_call_credentials *c = (grpc_composite_call_credentials *)creds;
   grpc_composite_call_credentials_metadata_context *ctx;
 
   ctx = gpr_malloc(sizeof(grpc_composite_call_credentials_metadata_context));
   memset(ctx, 0, sizeof(grpc_composite_call_credentials_metadata_context));
-  ctx->service_url = gpr_strdup(service_url);
+  ctx->auth_md_context = auth_md_context;
   ctx->user_data = user_data;
   ctx->cb = cb;
   ctx->composite_creds = c;
   ctx->pollset = pollset;
   ctx->md_elems = grpc_credentials_md_store_create(c->inner.num_creds);
   grpc_call_credentials_get_request_metadata(
-      exec_ctx, c->inner.creds_array[ctx->creds_index++], pollset, service_url,
-      composite_call_metadata_cb, ctx);
+      exec_ctx, c->inner.creds_array[ctx->creds_index++], pollset,
+      auth_md_context, composite_call_metadata_cb, ctx);
 }
 
 static grpc_call_credentials_vtable composite_call_credentials_vtable = {
@@ -1089,7 +1095,7 @@ static void iam_destruct(grpc_call_credentials *creds) {
 static void iam_get_request_metadata(grpc_exec_ctx *exec_ctx,
                                      grpc_call_credentials *creds,
                                      grpc_pollset *pollset,
-                                     const char *service_url,
+                                     grpc_auth_metadata_context context,
                                      grpc_credentials_metadata_cb cb,
                                      void *user_data) {
   grpc_google_iam_credentials *c = (grpc_google_iam_credentials *)creds;
@@ -1098,7 +1104,7 @@ static void iam_get_request_metadata(grpc_exec_ctx *exec_ctx,
 }
 
 static grpc_call_credentials_vtable iam_vtable = {iam_destruct,
-                                             iam_get_request_metadata};
+                                                  iam_get_request_metadata};
 
 grpc_call_credentials *grpc_google_iam_credentials_create(
     const char *token, const char *authority_selector, void *reserved) {
@@ -1178,7 +1184,7 @@ static void plugin_md_request_metadata_ready(void *request,
 static void plugin_get_request_metadata(grpc_exec_ctx *exec_ctx,
                                         grpc_call_credentials *creds,
                                         grpc_pollset *pollset,
-                                        const char *service_url,
+                                        grpc_auth_metadata_context context,
                                         grpc_credentials_metadata_cb cb,
                                         void *user_data) {
   grpc_plugin_credentials *c = (grpc_plugin_credentials *)creds;
@@ -1187,7 +1193,7 @@ static void plugin_get_request_metadata(grpc_exec_ctx *exec_ctx,
     memset(request, 0, sizeof(*request));
     request->user_data = user_data;
     request->cb = cb;
-    c->plugin.get_metadata(c->plugin.state, service_url,
+    c->plugin.get_metadata(c->plugin.state, context,
                            plugin_md_request_metadata_ready, request);
   } else {
     cb(exec_ctx, user_data, NULL, 0, GRPC_CREDENTIALS_OK);
@@ -1204,7 +1210,7 @@ grpc_call_credentials *grpc_metadata_credentials_create_from_plugin(
                  (reserved));
   GPR_ASSERT(reserved == NULL);
   memset(c, 0, sizeof(*c));
-  c->base.type = GRPC_CALL_CREDENTIALS_TYPE_METADATA_PLUGIN;
+  c->base.type = plugin.type;
   c->base.vtable = &plugin_vtable;
   gpr_ref_init(&c->base.refcount, 1);
   c->plugin = plugin;

src/core/security/credentials.h

@@ -59,7 +59,6 @@ typedef enum {
   "FakeTransportSecurity"
 
 #define GRPC_CALL_CREDENTIALS_TYPE_OAUTH2 "Oauth2"
-#define GRPC_CALL_CREDENTIALS_TYPE_METADATA_PLUGIN "Plugin"
 #define GRPC_CALL_CREDENTIALS_TYPE_JWT "Jwt"
 #define GRPC_CALL_CREDENTIALS_TYPE_IAM "Iam"
 #define GRPC_CALL_CREDENTIALS_TYPE_COMPOSITE "Composite"
@@ -162,7 +161,7 @@ typedef struct {
   void (*destruct)(grpc_call_credentials *c);
   void (*get_request_metadata)(grpc_exec_ctx *exec_ctx,
                                grpc_call_credentials *c, grpc_pollset *pollset,
-                               const char *service_url,
+                               grpc_auth_metadata_context context,
                                grpc_credentials_metadata_cb cb,
                                void *user_data);
 } grpc_call_credentials_vtable;
@@ -178,7 +177,7 @@ void grpc_call_credentials_unref(grpc_call_credentials *creds);
 void grpc_call_credentials_get_request_metadata(grpc_exec_ctx *exec_ctx,
                                                 grpc_call_credentials *creds,
                                                 grpc_pollset *pollset,
-                                                const char *service_url,
+                                                grpc_auth_metadata_context context,
                                                 grpc_credentials_metadata_cb cb,
                                                 void *user_data);
 

src/cpp/client/secure_credentials.cc

@@ -160,7 +160,7 @@ void MetadataCredentialsPluginWrapper::Destroy(void* wrapper) {
 }
 
 void MetadataCredentialsPluginWrapper::GetMetadata(
-    void* wrapper, const char* service_url,
+    void* wrapper, grpc_auth_metadata_context context,
     grpc_credentials_plugin_metadata_cb cb, void* user_data) {
   GPR_ASSERT(wrapper);
   MetadataCredentialsPluginWrapper* w =
@@ -172,9 +172,9 @@ void MetadataCredentialsPluginWrapper::GetMetadata(
   if (w->plugin_->IsBlocking()) {
     w->thread_pool_->Add(
         std::bind(&MetadataCredentialsPluginWrapper::InvokePlugin, w,
-                  service_url, cb, user_data));
+                  context.service_url, cb, user_data));
   } else {
-    w->InvokePlugin(service_url, cb, user_data);
+    w->InvokePlugin(context.service_url, cb, user_data);
   }
 }
 
@@ -208,7 +208,7 @@ std::shared_ptr<CallCredentials> MetadataCredentialsFromPlugin(
       new MetadataCredentialsPluginWrapper(std::move(plugin));
   grpc_metadata_credentials_plugin c_plugin = {
       MetadataCredentialsPluginWrapper::GetMetadata,
-      MetadataCredentialsPluginWrapper::Destroy, wrapper};
+      MetadataCredentialsPluginWrapper::Destroy, wrapper, ""};
   return WrapCallCredentials(
       grpc_metadata_credentials_create_from_plugin(c_plugin, nullptr));
 }

src/cpp/client/secure_credentials.h

@@ -80,7 +80,7 @@ class SecureCallCredentials GRPC_FINAL : public CallCredentials {
 class MetadataCredentialsPluginWrapper GRPC_FINAL {
  public:
   static void Destroy(void* wrapper);
-  static void GetMetadata(void* wrapper, const char* service_url,
+  static void GetMetadata(void* wrapper, grpc_auth_metadata_context context,
                           grpc_credentials_plugin_metadata_cb cb,
                           void* user_data);
 

src/csharp/ext/grpc_csharp_ext.c

@@ -930,11 +930,12 @@ typedef void(GPR_CALLTYPE *grpcsharp_metadata_interceptor_func)(
   void *state, const char *service_url, grpc_credentials_plugin_metadata_cb cb,
   void *user_data, gpr_int32 is_destroy);
 
-static void grpcsharp_get_metadata_handler(void *state, const char *service_url,
-  grpc_credentials_plugin_metadata_cb cb, void *user_data) {
+static void grpcsharp_get_metadata_handler(
+    void *state, grpc_auth_metadata_context context,
+    grpc_credentials_plugin_metadata_cb cb, void *user_data) {
   grpcsharp_metadata_interceptor_func interceptor =
       (grpcsharp_metadata_interceptor_func)(gpr_intptr)state;
-  interceptor(state, service_url, cb, user_data, 0);
+  interceptor(state, context.service_url, cb, user_data, 0);
 }
 
 static void grpcsharp_metadata_credentials_destroy_handler(void *state) {
@@ -949,6 +950,7 @@ GPR_EXPORT grpc_call_credentials *GPR_CALLTYPE grpcsharp_metadata_credentials_cr
   plugin.get_metadata = grpcsharp_get_metadata_handler;
   plugin.destroy = grpcsharp_metadata_credentials_destroy_handler;
   plugin.state = (void*)(gpr_intptr)metadata_interceptor;
+  plugin.type = "";
   return grpc_metadata_credentials_create_from_plugin(plugin, NULL);
 }
 

src/node/ext/call_credentials.cc

@@ -162,6 +162,7 @@ NAN_METHOD(CallCredentials::CreateFromPlugin) {
   plugin.get_metadata = plugin_get_metadata;
   plugin.destroy = plugin_destroy_state;
   plugin.state = reinterpret_cast<void*>(state);
+  plugin.type = "";
   grpc_call_credentials *creds = grpc_metadata_credentials_create_from_plugin(
       plugin, NULL);
   info.GetReturnValue().Set(WrapStruct(creds));
@@ -225,7 +226,7 @@ NAUV_WORK_CB(SendPluginCallback) {
   uv_close((uv_handle_t *)async, (uv_close_cb)free);
 }
 
-void plugin_get_metadata(void *state, const char *service_url,
+void plugin_get_metadata(void *state, grpc_auth_metadata_context context,
                          grpc_credentials_plugin_metadata_cb cb,
                          void *user_data) {
   uv_async_t *async = static_cast<uv_async_t*>(malloc(sizeof(uv_async_t)));
@@ -234,7 +235,7 @@ void plugin_get_metadata(void *state, const char *service_url,
                 SendPluginCallback);
   plugin_callback_data *data = new plugin_callback_data;
   data->state = reinterpret_cast<plugin_state*>(state);
-  data->service_url = service_url;
+  data->service_url = context.service_url;
   data->cb = cb;
   data->user_data = user_data;
   async->data = data;

src/node/ext/call_credentials.h

@@ -84,7 +84,7 @@ typedef struct plugin_callback_data {
   void *user_data;
 } plugin_callback_data;
 
-void plugin_get_metadata(void *state, const char *service_url,
+void plugin_get_metadata(void *state, grpc_auth_metadata_context context,
                          grpc_credentials_plugin_metadata_cb cb,
                          void *user_data);
 

test/core/security/credentials_test.c

@@ -126,6 +126,8 @@ static const char test_signed_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_method[] = "ThisIsNotAMethod";
+
 /* -- Utils. -- */
 
 static char *test_json_key_str(void) {
@@ -352,9 +354,10 @@ static void test_google_iam_creds(void) {
   grpc_call_credentials *creds = grpc_google_iam_credentials_create(
       test_google_iam_authorization_token, test_google_iam_authority_selector,
       NULL);
-  grpc_call_credentials_get_request_metadata(&exec_ctx, creds, NULL,
-                                        test_service_url,
-                                        check_google_iam_metadata, creds);
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
+  grpc_call_credentials_get_request_metadata(
+      &exec_ctx, creds, NULL, auth_md_ctx, check_google_iam_metadata, creds);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
@@ -375,9 +378,11 @@ static void test_access_token_creds(void) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_call_credentials *creds =
       grpc_access_token_credentials_create("blah", NULL);
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   GPR_ASSERT(strcmp(creds->type, GRPC_CALL_CREDENTIALS_TYPE_OAUTH2) == 0);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, creds, NULL, test_service_url, check_access_token_metadata,
+      &exec_ctx, creds, NULL, auth_md_ctx, check_access_token_metadata,
       creds);
   grpc_exec_ctx_finish(&exec_ctx);
 }
@@ -430,6 +435,8 @@ static void check_oauth2_google_iam_composite_metadata(
 static void test_oauth2_google_iam_composite_creds(void) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   const grpc_call_credentials_array *creds_array;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   grpc_call_credentials *oauth2_creds = grpc_md_only_test_credentials_create(
       "authorization", test_oauth2_bearer_token, 0);
   grpc_call_credentials *google_iam_creds = grpc_google_iam_credentials_create(
@@ -449,7 +456,7 @@ static void test_oauth2_google_iam_composite_creds(void) {
   GPR_ASSERT(strcmp(creds_array->creds_array[1]->type,
                     GRPC_CALL_CREDENTIALS_TYPE_IAM) == 0);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, composite_creds, NULL, test_service_url,
+      &exec_ctx, composite_creds, NULL, auth_md_ctx,
       check_oauth2_google_iam_composite_metadata, composite_creds);
   grpc_exec_ctx_finish(&exec_ctx);
 }
@@ -576,12 +583,14 @@ static void test_compute_engine_creds_success(void) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_call_credentials *compute_engine_creds =
       grpc_google_compute_engine_credentials_create(NULL);
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
 
   /* First request: http get should be called. */
   grpc_httpcli_set_override(compute_engine_httpcli_get_success_override,
                             httpcli_post_should_not_be_called);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, compute_engine_creds, NULL, test_service_url,
+      &exec_ctx, compute_engine_creds, NULL, auth_md_ctx,
       on_oauth2_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_flush(&exec_ctx);
 
@@ -589,7 +598,7 @@ static void test_compute_engine_creds_success(void) {
   grpc_httpcli_set_override(httpcli_get_should_not_be_called,
                             httpcli_post_should_not_be_called);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, compute_engine_creds, NULL, test_service_url,
+      &exec_ctx, compute_engine_creds, NULL, auth_md_ctx,
       on_oauth2_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_finish(&exec_ctx);
 
@@ -599,12 +608,14 @@ static void test_compute_engine_creds_success(void) {
 
 static void test_compute_engine_creds_failure(void) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   grpc_call_credentials *compute_engine_creds =
       grpc_google_compute_engine_credentials_create(NULL);
   grpc_httpcli_set_override(compute_engine_httpcli_get_failure_override,
                             httpcli_post_should_not_be_called);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, compute_engine_creds, NULL, test_service_url,
+      &exec_ctx, compute_engine_creds, NULL, auth_md_ctx,
       on_oauth2_creds_get_metadata_failure, (void *)test_user_data);
   grpc_call_credentials_unref(compute_engine_creds);
   grpc_httpcli_set_override(NULL, NULL);
@@ -656,6 +667,8 @@ static int refresh_token_httpcli_post_failure(
 
 static void test_refresh_token_creds_success(void) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   grpc_call_credentials *refresh_token_creds =
       grpc_google_refresh_token_credentials_create(test_refresh_token_str,
                                                    NULL);
@@ -664,7 +677,7 @@ static void test_refresh_token_creds_success(void) {
   grpc_httpcli_set_override(httpcli_get_should_not_be_called,
                             refresh_token_httpcli_post_success);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, refresh_token_creds, NULL, test_service_url,
+      &exec_ctx, refresh_token_creds, NULL, auth_md_ctx,
       on_oauth2_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_flush(&exec_ctx);
 
@@ -672,7 +685,7 @@ static void test_refresh_token_creds_success(void) {
   grpc_httpcli_set_override(httpcli_get_should_not_be_called,
                             httpcli_post_should_not_be_called);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, refresh_token_creds, NULL, test_service_url,
+      &exec_ctx, refresh_token_creds, NULL, auth_md_ctx,
       on_oauth2_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_flush(&exec_ctx);
 
@@ -683,13 +696,15 @@ static void test_refresh_token_creds_success(void) {
 
 static void test_refresh_token_creds_failure(void) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   grpc_call_credentials *refresh_token_creds =
       grpc_google_refresh_token_credentials_create(test_refresh_token_str,
                                                    NULL);
   grpc_httpcli_set_override(httpcli_get_should_not_be_called,
                             refresh_token_httpcli_post_failure);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, refresh_token_creds, NULL, test_service_url,
+      &exec_ctx, refresh_token_creds, NULL, auth_md_ctx,
       on_oauth2_creds_get_metadata_failure, (void *)test_user_data);
   grpc_call_credentials_unref(refresh_token_creds);
   grpc_httpcli_set_override(NULL, NULL);
@@ -772,6 +787,8 @@ static void on_jwt_creds_get_metadata_failure(grpc_exec_ctx *exec_ctx,
 static void test_jwt_creds_success(void) {
   char *json_key_string = test_json_key_str();
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   grpc_call_credentials *jwt_creds =
       grpc_service_account_jwt_access_credentials_create(
           json_key_string, grpc_max_auth_token_lifetime, NULL);
@@ -779,7 +796,7 @@ static void test_jwt_creds_success(void) {
   /* First request: jwt_encode_and_sign should be called. */
   grpc_jwt_encode_and_sign_set_override(encode_and_sign_jwt_success);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, jwt_creds, NULL, test_service_url,
+      &exec_ctx, jwt_creds, NULL, auth_md_ctx,
       on_jwt_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_flush(&exec_ctx);
 
@@ -787,15 +804,16 @@ static void test_jwt_creds_success(void) {
   grpc_jwt_encode_and_sign_set_override(
       encode_and_sign_jwt_should_not_be_called);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, jwt_creds, NULL, test_service_url,
+      &exec_ctx, jwt_creds, NULL, auth_md_ctx,
       on_jwt_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_flush(&exec_ctx);
 
   /* Third request: Different service url so jwt_encode_and_sign should be
      called again (no caching). */
+  auth_md_ctx.service_url = other_test_service_url;
   grpc_jwt_encode_and_sign_set_override(encode_and_sign_jwt_success);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, jwt_creds, NULL, other_test_service_url,
+      &exec_ctx, jwt_creds, NULL, auth_md_ctx,
       on_jwt_creds_get_metadata_success, (void *)test_user_data);
   grpc_exec_ctx_flush(&exec_ctx);
 
@@ -807,13 +825,15 @@ static void test_jwt_creds_success(void) {
 static void test_jwt_creds_signing_failure(void) {
   char *json_key_string = test_json_key_str();
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
   grpc_call_credentials *jwt_creds =
       grpc_service_account_jwt_access_credentials_create(
           json_key_string, grpc_max_auth_token_lifetime, NULL);
 
   grpc_jwt_encode_and_sign_set_override(encode_and_sign_jwt_failure);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, jwt_creds, NULL, test_service_url,
+      &exec_ctx, jwt_creds, NULL, auth_md_ctx,
       on_jwt_creds_get_metadata_failure, (void *)test_user_data);
 
   gpr_free(json_key_string);
@@ -884,13 +904,17 @@ typedef struct {
 
 static const plugin_metadata plugin_md[] = {{"foo", "bar"}, {"hi", "there"}};
 
-static void plugin_get_metadata_success(void *state, const char *service_url,
+static void plugin_get_metadata_success(void *state,
+                                        grpc_auth_metadata_context context,
                                         grpc_credentials_plugin_metadata_cb cb,
                                         void *user_data) {
   size_t i;
   grpc_metadata md[GPR_ARRAY_SIZE(plugin_md)];
   plugin_state *s = (plugin_state *)state;
-  GPR_ASSERT(strcmp(service_url, test_service_url) == 0);
+  GPR_ASSERT(strcmp(context.service_url, test_service_url) == 0);
+  GPR_ASSERT(strcmp(context.method_name, test_method) == 0);
+  GPR_ASSERT(context.channel_auth_context == NULL);
+  GPR_ASSERT(context.reserved == NULL);
   *s = PLUGIN_GET_METADATA_CALLED_STATE;
   for (i = 0; i < GPR_ARRAY_SIZE(plugin_md); i++) {
     memset(&md[i], 0, sizeof(grpc_metadata));
@@ -901,11 +925,15 @@ static void plugin_get_metadata_success(void *state, const char *service_url,
   cb(user_data, md, GPR_ARRAY_SIZE(md), GRPC_STATUS_OK, NULL);
 }
 
-static void plugin_get_metadata_failure(void *state, const char *service_url,
+static void plugin_get_metadata_failure(void *state,
+                                        grpc_auth_metadata_context context,
                                         grpc_credentials_plugin_metadata_cb cb,
                                         void *user_data) {
   plugin_state *s = (plugin_state *)state;
-  GPR_ASSERT(strcmp(service_url, test_service_url) == 0);
+  GPR_ASSERT(strcmp(context.service_url, test_service_url) == 0);
+  GPR_ASSERT(strcmp(context.method_name, test_method) == 0);
+  GPR_ASSERT(context.channel_auth_context == NULL);
+  GPR_ASSERT(context.reserved == NULL);
   *s = PLUGIN_GET_METADATA_CALLED_STATE;
   cb(user_data, NULL, 0, GRPC_STATUS_UNAUTHENTICATED,
      "Could not get metadata for plugin.");
@@ -943,6 +971,8 @@ static void test_metadata_plugin_success(void) {
   plugin_state state = PLUGIN_INITIAL_STATE;
   grpc_metadata_credentials_plugin plugin;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
 
   plugin.state = &state;
   plugin.get_metadata = plugin_get_metadata_success;
@@ -951,7 +981,7 @@ static void test_metadata_plugin_success(void) {
   creds = grpc_metadata_credentials_create_from_plugin(plugin, NULL);
   GPR_ASSERT(state == PLUGIN_INITIAL_STATE);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, creds, NULL, test_service_url,
+      &exec_ctx, creds, NULL, auth_md_ctx,
       on_plugin_metadata_received_success, NULL);
   GPR_ASSERT(state == PLUGIN_GET_METADATA_CALLED_STATE);
   grpc_call_credentials_release(creds);
@@ -964,6 +994,8 @@ static void test_metadata_plugin_failure(void) {
   plugin_state state = PLUGIN_INITIAL_STATE;
   grpc_metadata_credentials_plugin plugin;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_auth_metadata_context auth_md_ctx = {test_service_url, test_method, NULL,
+                                            NULL};
 
   plugin.state = &state;
   plugin.get_metadata = plugin_get_metadata_failure;
@@ -972,7 +1004,7 @@ static void test_metadata_plugin_failure(void) {
   creds = grpc_metadata_credentials_create_from_plugin(plugin, NULL);
   GPR_ASSERT(state == PLUGIN_INITIAL_STATE);
   grpc_call_credentials_get_request_metadata(
-      &exec_ctx, creds, NULL, test_service_url,
+      &exec_ctx, creds, NULL, auth_md_ctx,
       on_plugin_metadata_received_failure, NULL);
   GPR_ASSERT(state == PLUGIN_GET_METADATA_CALLED_STATE);
   grpc_call_credentials_release(creds);

test/core/security/oauth2_utils.c

@@ -80,13 +80,15 @@ char *grpc_test_fetch_oauth2_token_with_credentials(
   oauth2_request request;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_closure do_nothing_closure;
+  grpc_auth_metadata_context null_ctx = {"", "", NULL, NULL};
+
   grpc_pollset_init(&request.pollset);
   request.is_done = 0;
 
   grpc_closure_init(&do_nothing_closure, do_nothing, NULL);
 
   grpc_call_credentials_get_request_metadata(&exec_ctx, creds, &request.pollset,
-                                             "", on_oauth2_response, &request);
+                                             null_ctx, on_oauth2_response, &request);
 
   grpc_exec_ctx_finish(&exec_ctx);
 

test/core/security/print_google_default_creds_token.c

@@ -74,10 +74,13 @@ int main(int argc, char **argv) {
   synchronizer sync;
   grpc_channel_credentials *creds = NULL;
   char *service_url = "https://test.foo.google.com/Foo";
+  grpc_auth_metadata_context context;
   gpr_cmdline *cl = gpr_cmdline_create("print_google_default_creds_token");
   gpr_cmdline_add_string(cl, "service_url",
                          "Service URL for the token request.", &service_url);
   gpr_cmdline_parse(cl, argc, argv);
+  memset(&context, 0, sizeof(context));
+  context.service_url = service_url;
 
   grpc_init();
 
@@ -93,7 +96,7 @@ int main(int argc, char **argv) {
 
   grpc_call_credentials_get_request_metadata(
       &exec_ctx, ((grpc_composite_channel_credentials *)creds)->call_creds,
-      &sync.pollset, service_url, on_metadata_response, &sync);
+      &sync.pollset, context, on_metadata_response, &sync);
 
   gpr_mu_lock(GRPC_POLLSET_MU(&sync.pollset));
   while (!sync.is_done) {