Server auth metadata processor.

- Right now it is a global function: would be better to have this per
  (secure) port.
- Changed the interface of the auth_context slightly to make it more
  friendly.
- Positive tests pass. Still need some work on error case (have a
  negative case as well).
- Fixing cpp auth context tests so that they use the shiny new C API.

7 files changed, 297 insertions, 99 deletions

diff --git a/src/core/security/credentials.c b/src/core/security/credentials.c
index 230f0dfb85..71513bcc25 100644
--- a/src/core/security/credentials.c
+++ b/src/core/security/credentials.c
@@ -759,19 +759,19 @@ grpc_credentials *grpc_refresh_token_credentials_create(
       grpc_auth_refresh_token_create_from_string(json_refresh_token));
 }
 
-/* -- Fake Oauth2 credentials. -- */
+/* -- Metadata-only credentials. -- */
 
-static void fake_oauth2_destroy(grpc_credentials *creds) {
-  grpc_fake_oauth2_credentials *c = (grpc_fake_oauth2_credentials *)creds;
-  grpc_credentials_md_store_unref(c->access_token_md);
+static void md_only_test_destroy(grpc_credentials *creds) {
+  grpc_md_only_test_credentials *c = (grpc_md_only_test_credentials *)creds;
+  grpc_credentials_md_store_unref(c->md_store);
   gpr_free(c);
 }
 
-static int fake_oauth2_has_request_metadata(const grpc_credentials *creds) {
+static int md_only_test_has_request_metadata(const grpc_credentials *creds) {
   return 1;
 }
 
-static int fake_oauth2_has_request_metadata_only(
+static int md_only_test_has_request_metadata_only(
     const grpc_credentials *creds) {
   return 1;
 }
@@ -779,19 +779,19 @@ static int fake_oauth2_has_request_metadata_only(
 void on_simulated_token_fetch_done(void *user_data, int success) {
   grpc_credentials_metadata_request *r =
       (grpc_credentials_metadata_request *)user_data;
-  grpc_fake_oauth2_credentials *c = (grpc_fake_oauth2_credentials *)r->creds;
+  grpc_md_only_test_credentials *c = (grpc_md_only_test_credentials *)r->creds;
   GPR_ASSERT(success);
-  r->cb(r->user_data, c->access_token_md->entries,
-        c->access_token_md->num_entries, GRPC_CREDENTIALS_OK);
+  r->cb(r->user_data, c->md_store->entries,
+        c->md_store->num_entries, GRPC_CREDENTIALS_OK);
   grpc_credentials_metadata_request_destroy(r);
 }
 
-static void fake_oauth2_get_request_metadata(grpc_credentials *creds,
+static void md_only_test_get_request_metadata(grpc_credentials *creds,
                                              grpc_pollset *pollset,
                                              const char *service_url,
                                              grpc_credentials_metadata_cb cb,
                                              void *user_data) {
-  grpc_fake_oauth2_credentials *c = (grpc_fake_oauth2_credentials *)creds;
+  grpc_md_only_test_credentials *c = (grpc_md_only_test_credentials *)creds;
 
   if (c->is_async) {
     grpc_credentials_metadata_request *cb_arg =
@@ -800,26 +800,26 @@ static void fake_oauth2_get_request_metadata(grpc_credentials *creds,
                             on_simulated_token_fetch_done, cb_arg);
     grpc_iomgr_add_callback(cb_arg->on_simulated_token_fetch_done_closure);
   } else {
-    cb(user_data, c->access_token_md->entries, 1, GRPC_CREDENTIALS_OK);
+    cb(user_data, c->md_store->entries, 1, GRPC_CREDENTIALS_OK);
   }
 }
 
-static grpc_credentials_vtable fake_oauth2_vtable = {
-    fake_oauth2_destroy, fake_oauth2_has_request_metadata,
-    fake_oauth2_has_request_metadata_only, fake_oauth2_get_request_metadata,
+static grpc_credentials_vtable md_only_test_vtable = {
+    md_only_test_destroy, md_only_test_has_request_metadata,
+    md_only_test_has_request_metadata_only, md_only_test_get_request_metadata,
     NULL};
 
-grpc_credentials *grpc_fake_oauth2_credentials_create(
-    const char *token_md_value, int is_async) {
-  grpc_fake_oauth2_credentials *c =
-      gpr_malloc(sizeof(grpc_fake_oauth2_credentials));
-  memset(c, 0, sizeof(grpc_fake_oauth2_credentials));
+grpc_credentials *grpc_md_only_test_credentials_create(const char *md_key,
+                                                       const char *md_value,
+                                                       int is_async) {
+  grpc_md_only_test_credentials *c =
+      gpr_malloc(sizeof(grpc_md_only_test_credentials));
+  memset(c, 0, sizeof(grpc_md_only_test_credentials));
   c->base.type = GRPC_CREDENTIALS_TYPE_OAUTH2;
-  c->base.vtable = &fake_oauth2_vtable;
+  c->base.vtable = &md_only_test_vtable;
   gpr_ref_init(&c->base.refcount, 1);
-  c->access_token_md = grpc_credentials_md_store_create(1);
-  grpc_credentials_md_store_add_cstrings(
-      c->access_token_md, GRPC_AUTHORIZATION_METADATA_KEY, token_md_value);
+  c->md_store = grpc_credentials_md_store_create(1);
+  grpc_credentials_md_store_add_cstrings(c->md_store, md_key, md_value);
   c->is_async = is_async;
   return &c->base;
 }
diff --git a/src/core/security/credentials.h b/src/core/security/credentials.h
index d988901cf7..664524522b 100644
--- a/src/core/security/credentials.h
+++ b/src/core/security/credentials.h
@@ -182,9 +182,10 @@ grpc_oauth2_token_fetcher_credentials_parse_server_response(
     grpc_credentials_md_store **token_md, gpr_timespec *token_lifetime);
 void grpc_flush_cached_google_default_credentials(void);
 
-/* Simulates an oauth2 token fetch with the specified value for testing. */
-grpc_credentials *grpc_fake_oauth2_credentials_create(
-    const char *token_md_value, int is_async);
+/* Metadata-only credentials with the specified key and value where
+   asynchronicity can be simulated for testing. */
+grpc_credentials *grpc_md_only_test_credentials_create(
+    const char *md_key, const char *md_value, int is_async);
 
 /* Private constructor for jwt credentials from an already parsed json key.
    Takes ownership of the key. */
@@ -288,13 +289,13 @@ typedef struct {
   grpc_credentials_md_store *access_token_md;
 } grpc_access_token_credentials;
 
-/* -- Fake Oauth2 credentials. -- */
+/* --  Metadata-only Test credentials. -- */
 
 typedef struct {
   grpc_credentials base;
-  grpc_credentials_md_store *access_token_md;
+  grpc_credentials_md_store *md_store;
   int is_async;
-} grpc_fake_oauth2_credentials;
+} grpc_md_only_test_credentials;
 
 /* -- IAM credentials. -- */
 
diff --git a/src/core/security/security_connector.c b/src/core/security/security_connector.c
index f6e423eb27..8aee8f3ef4 100644
--- a/src/core/security/security_connector.c
+++ b/src/core/security/security_connector.c
@@ -263,9 +263,9 @@ static grpc_security_status fake_check_peer(grpc_security_connector *sc,
     goto end;
   }
   GRPC_AUTH_CONTEXT_UNREF(sc->auth_context, "connector");
-  sc->auth_context = grpc_auth_context_create(NULL, 1);
-  sc->auth_context->properties[0] = grpc_auth_property_init_from_cstring(
-      GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME,
+  sc->auth_context = grpc_auth_context_create(NULL);
+  grpc_auth_context_add_cstring_property(
+      sc->auth_context, GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME,
       GRPC_FAKE_TRANSPORT_SECURITY_TYPE);
 
 end:
@@ -409,31 +409,35 @@ static int ssl_host_matches_name(const tsi_peer *peer, const char *peer_name) {
 grpc_auth_context *tsi_ssl_peer_to_auth_context(const tsi_peer *peer) {
   size_t i;
   grpc_auth_context *ctx = NULL;
+  const char *peer_identity_property_name = NULL;
 
   /* The caller has checked the certificate type property. */
   GPR_ASSERT(peer->property_count >= 1);
-  ctx = grpc_auth_context_create(NULL, peer->property_count);
-  ctx->properties[0] = grpc_auth_property_init_from_cstring(
-      GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME,
+  ctx = grpc_auth_context_create(NULL);
+  grpc_auth_context_add_cstring_property(
+      ctx, GRPC_TRANSPORT_SECURITY_TYPE_PROPERTY_NAME,
       GRPC_SSL_TRANSPORT_SECURITY_TYPE);
-  ctx->property_count = 1;
   for (i = 0; i < peer->property_count; i++) {
     const tsi_peer_property *prop = &peer->properties[i];
     if (prop->name == NULL) continue;
     if (strcmp(prop->name, TSI_X509_SUBJECT_COMMON_NAME_PEER_PROPERTY) == 0) {
       /* If there is no subject alt name, have the CN as the identity. */
-      if (ctx->peer_identity_property_name == NULL) {
-        ctx->peer_identity_property_name = GRPC_X509_CN_PROPERTY_NAME;
+      if (peer_identity_property_name == NULL) {
+        peer_identity_property_name = GRPC_X509_CN_PROPERTY_NAME;
       }
-      ctx->properties[ctx->property_count++] = grpc_auth_property_init(
-          GRPC_X509_CN_PROPERTY_NAME, prop->value.data, prop->value.length);
+      grpc_auth_context_add_property(ctx, GRPC_X509_CN_PROPERTY_NAME,
+                                     prop->value.data, prop->value.length);
     } else if (strcmp(prop->name,
                       TSI_X509_SUBJECT_ALTERNATIVE_NAME_PEER_PROPERTY) == 0) {
-      ctx->peer_identity_property_name = GRPC_X509_SAN_PROPERTY_NAME;
-      ctx->properties[ctx->property_count++] = grpc_auth_property_init(
-          GRPC_X509_SAN_PROPERTY_NAME, prop->value.data, prop->value.length);
+      peer_identity_property_name = GRPC_X509_SAN_PROPERTY_NAME;
+      grpc_auth_context_add_property(ctx, GRPC_X509_SAN_PROPERTY_NAME,
+                                     prop->value.data, prop->value.length);
     }
   }
+  if (peer_identity_property_name != NULL) {
+    GPR_ASSERT(grpc_auth_context_set_peer_identity_property_name(
+                   ctx, peer_identity_property_name) == 1);
+  }
   return ctx;
 }
 
diff --git a/src/core/security/security_context.c b/src/core/security/security_context.c
index 8ce7876bd8..0015d5b915 100644
--- a/src/core/security/security_context.c
+++ b/src/core/security/security_context.c
@@ -42,6 +42,20 @@
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 
+/* --- grpc_process_auth_metadata_func --- */
+
+static grpc_process_auth_metadata_func server_md_func = NULL;
+
+void grpc_server_auth_context_register_process_metadata_func(
+    grpc_process_auth_metadata_func func) {
+  server_md_func = func;
+}
+
+grpc_process_auth_metadata_func
+grpc_server_auth_context_get_process_metadata_func(void) {
+  return server_md_func;
+}
+
 /* --- grpc_call --- */
 
 grpc_call_error grpc_call_set_credentials(grpc_call *call,
@@ -120,15 +134,15 @@ void grpc_server_security_context_destroy(void *ctx) {
 
 static grpc_auth_property_iterator empty_iterator = {NULL, 0, NULL};
 
-grpc_auth_context *grpc_auth_context_create(grpc_auth_context *chained,
-                                            size_t property_count) {
+grpc_auth_context *grpc_auth_context_create(grpc_auth_context *chained) {
   grpc_auth_context *ctx = gpr_malloc(sizeof(grpc_auth_context));
   memset(ctx, 0, sizeof(grpc_auth_context));
-  ctx->properties = gpr_malloc(property_count * sizeof(grpc_auth_property));
-  memset(ctx->properties, 0, property_count * sizeof(grpc_auth_property));
-  ctx->property_count = property_count;
   gpr_ref_init(&ctx->refcount, 1);
-  if (chained != NULL) ctx->chained = GRPC_AUTH_CONTEXT_REF(chained, "chained");
+  if (chained != NULL) {
+    ctx->chained = GRPC_AUTH_CONTEXT_REF(chained, "chained");
+    ctx->peer_identity_property_name =
+        ctx->chained->peer_identity_property_name;
+  }
   return ctx;
 }
 
@@ -162,11 +176,11 @@ void grpc_auth_context_unref(grpc_auth_context *ctx) {
   if (gpr_unref(&ctx->refcount)) {
     size_t i;
     GRPC_AUTH_CONTEXT_UNREF(ctx->chained, "chained");
-    if (ctx->properties != NULL) {
-      for (i = 0; i < ctx->property_count; i++) {
-        grpc_auth_property_reset(&ctx->properties[i]);
+    if (ctx->properties.array != NULL) {
+      for (i = 0; i < ctx->properties.count; i++) {
+        grpc_auth_property_reset(&ctx->properties.array[i]);
       }
-      gpr_free(ctx->properties);
+      gpr_free(ctx->properties.array);
     }
     gpr_free(ctx);
   }
@@ -177,6 +191,20 @@ const char *grpc_auth_context_peer_identity_property_name(
   return ctx->peer_identity_property_name;
 }
 
+int grpc_auth_context_set_peer_identity_property_name(grpc_auth_context *ctx,
+                                                      const char *name) {
+  grpc_auth_property_iterator it =
+      grpc_auth_context_find_properties_by_name(ctx, name);
+  const grpc_auth_property *prop = grpc_auth_property_iterator_next(&it);
+  if (prop == NULL) {
+    gpr_log(GPR_ERROR, "Property name %s not found in auth context.",
+            name != NULL ? name : "NULL");
+    return 0;
+  }
+  ctx->peer_identity_property_name = prop->name;
+  return 1;
+}
+
 int grpc_auth_context_peer_is_authenticated(
     const grpc_auth_context *ctx) {
   return ctx->peer_identity_property_name == NULL ? 0 : 1;
@@ -193,16 +221,16 @@ grpc_auth_property_iterator grpc_auth_context_property_iterator(
 const grpc_auth_property *grpc_auth_property_iterator_next(
     grpc_auth_property_iterator *it) {
   if (it == NULL || it->ctx == NULL) return NULL;
-  while (it->index == it->ctx->property_count) {
+  while (it->index == it->ctx->properties.count) {
     if (it->ctx->chained == NULL) return NULL;
     it->ctx = it->ctx->chained;
     it->index = 0;
   }
   if (it->name == NULL) {
-    return &it->ctx->properties[it->index++];
+    return &it->ctx->properties.array[it->index++];
   } else {
-    while (it->index < it->ctx->property_count) {
-      const grpc_auth_property *prop = &it->ctx->properties[it->index++];
+    while (it->index < it->ctx->properties.count) {
+      const grpc_auth_property *prop = &it->ctx->properties.array[it->index++];
       GPR_ASSERT(prop->name != NULL);
       if (strcmp(it->name, prop->name) == 0) {
         return prop;
@@ -229,24 +257,37 @@ grpc_auth_property_iterator grpc_auth_context_peer_identity(
       ctx, ctx->peer_identity_property_name);
 }
 
-grpc_auth_property grpc_auth_property_init_from_cstring(const char *name,
-                                                        const char *value) {
-  grpc_auth_property prop;
-  prop.name = gpr_strdup(name);
-  prop.value = gpr_strdup(value);
-  prop.value_length = strlen(value);
-  return prop;
+static void ensure_auth_context_capacity(grpc_auth_context *ctx) {
+  if (ctx->properties.count == ctx->properties.capacity) {
+    ctx->properties.capacity =
+        GPR_MAX(ctx->properties.capacity + 8, ctx->properties.capacity * 2);
+    ctx->properties.array =
+        gpr_realloc(ctx->properties.array,
+                    ctx->properties.capacity * sizeof(grpc_auth_property));
+  }
+}
+
+void grpc_auth_context_add_property(grpc_auth_context *ctx, const char *name,
+                                    const char *value, size_t value_length) {
+  grpc_auth_property *prop;
+  ensure_auth_context_capacity(ctx);
+  prop = &ctx->properties.array[ctx->properties.count++];
+  prop->name = gpr_strdup(name);
+  prop->value = gpr_malloc(value_length + 1);
+  memcpy(prop->value, value, value_length);
+  prop->value[value_length] = '\0';
+  prop->value_length = value_length;
 }
 
-grpc_auth_property grpc_auth_property_init(const char *name, const char *value,
-                                           size_t value_length) {
-  grpc_auth_property prop;
-  prop.name = gpr_strdup(name);
-  prop.value = gpr_malloc(value_length + 1);
-  memcpy(prop.value, value, value_length);
-  prop.value[value_length] = '\0';
-  prop.value_length = value_length;
-  return prop;
+void grpc_auth_context_add_cstring_property(grpc_auth_context *ctx,
+                                            const char *name,
+                                            const char *value) {
+  grpc_auth_property *prop;
+  ensure_auth_context_capacity(ctx);
+  prop = &ctx->properties.array[ctx->properties.count++];
+  prop->name = gpr_strdup(name);
+  prop->value = gpr_strdup(value);
+  prop->value_length = strlen(value);
 }
 
 void grpc_auth_property_reset(grpc_auth_property *property) {
diff --git a/src/core/security/security_context.h b/src/core/security/security_context.h
index 76a45910bb..b5dfae0666 100644
--- a/src/core/security/security_context.h
+++ b/src/core/security/security_context.h
@@ -34,11 +34,13 @@
 #ifndef GRPC_INTERNAL_CORE_SECURITY_SECURITY_CONTEXT_H
 #define GRPC_INTERNAL_CORE_SECURITY_SECURITY_CONTEXT_H
 
+#include "src/core/iomgr/pollset.h"
 #include "src/core/security/credentials.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+/* --- grpc_auth_ticket --- */
+struct grpc_auth_ticket {
+  grpc_pollset *pollset;
+};
 
 /* --- grpc_auth_context ---
 
@@ -46,18 +48,19 @@ extern "C" {
 
 /* Property names are always NULL terminated. */
 
+typedef struct {
+  grpc_auth_property *array;
+  size_t count;
+  size_t capacity;
+} grpc_auth_property_array;
+
 struct grpc_auth_context {
   struct grpc_auth_context *chained;
-  grpc_auth_property *properties;
-  size_t property_count;
+  grpc_auth_property_array properties;
   gpr_refcount refcount;
   const char *peer_identity_property_name;
 };
 
-/* Constructor. */
-grpc_auth_context *grpc_auth_context_create(grpc_auth_context *chained,
-                                            size_t property_count);
-
 /* Refcounting. */
 #ifdef GRPC_AUTH_CONTEXT_REFCOUNT_DEBUG
 #define GRPC_AUTH_CONTEXT_REF(p, r) \
@@ -76,12 +79,6 @@ grpc_auth_context *grpc_auth_context_ref(grpc_auth_context *policy);
 void grpc_auth_context_unref(grpc_auth_context *policy);
 #endif
 
-grpc_auth_property grpc_auth_property_init_from_cstring(const char *name,
-                                                        const char *value);
-
-grpc_auth_property grpc_auth_property_init(const char *name, const char *value,
-                                           size_t value_length);
-
 void grpc_auth_property_reset(grpc_auth_property *property);
 
 /* --- grpc_client_security_context ---
@@ -107,9 +104,10 @@ typedef struct {
 grpc_server_security_context *grpc_server_security_context_create(void);
 void grpc_server_security_context_destroy(void *ctx);
 
-#ifdef __cplusplus
-}
-#endif
+/* --- Auth metadata processing. --- */
+
+grpc_process_auth_metadata_func
+grpc_server_auth_context_get_process_metadata_func(void);
 
 #endif  /* GRPC_INTERNAL_CORE_SECURITY_SECURITY_CONTEXT_H */
 
diff --git a/src/core/security/server_auth_filter.c b/src/core/security/server_auth_filter.c
index 10eef6d237..fe993e50ee 100644
--- a/src/core/security/server_auth_filter.c
+++ b/src/core/security/server_auth_filter.c
@@ -31,20 +31,161 @@
  *
  */
 
+#include <string.h>
+
 #include "src/core/security/auth_filters.h"
 #include "src/core/security/security_connector.h"
 #include "src/core/security/security_context.h"
 
+#include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
 typedef struct call_data {
-  int unused; /* C89 requires at least one struct element */
+  gpr_uint8 got_client_metadata;
+  gpr_uint8 sent_status;
+  gpr_uint8 success;
+  grpc_linked_mdelem status;
+  grpc_stream_op_buffer *recv_ops;
+  /* Closure to call when finished with the hs_on_recv hook. */
+  grpc_iomgr_closure *on_done_recv;
+  /* Receive closures are chained: we inject this closure as the on_done_recv
+     up-call on transport_op, and remember to call our on_done_recv member after
+     handling it. */
+  grpc_iomgr_closure auth_on_recv;
+  const grpc_metadata *consumed_md;
+  size_t num_consumed_md;
+  grpc_stream_op *md_op;
+  grpc_auth_context **call_auth_context;
+  grpc_auth_ticket ticket;
 } call_data;
 
 typedef struct channel_data {
   grpc_security_connector *security_connector;
+  grpc_mdelem *status_auth_failure;
 } channel_data;
 
+static grpc_metadata_array metadata_batch_to_md_array(
+    const grpc_metadata_batch *batch) {
+  grpc_linked_mdelem *l;
+  grpc_metadata_array result;
+  grpc_metadata_array_init(&result);
+  for (l = batch->list.head; l != NULL; l = l->next) {
+    grpc_metadata *usr_md = NULL;
+    grpc_mdelem *md = l->md;
+    grpc_mdstr *key = md->key;
+    grpc_mdstr *value = md->value;
+    if (result.count == result.capacity) {
+      result.capacity = GPR_MAX(result.capacity + 8, result.capacity * 2);
+      result.metadata =
+          gpr_realloc(result.metadata, result.capacity * sizeof(grpc_metadata));
+    }
+    usr_md = &result.metadata[result.count++];
+    usr_md->key = grpc_mdstr_as_c_string(key);
+    usr_md->value = grpc_mdstr_as_c_string(value);
+    usr_md->value_length = GPR_SLICE_LENGTH(value->slice);
+  }
+  return result;
+}
+
+static grpc_mdelem *remove_consumed_md(void *user_data, grpc_mdelem *md) {
+  grpc_call_element *elem = user_data;
+  call_data *calld = elem->call_data;
+  size_t i;
+  for (i = 0; i < calld->num_consumed_md; i++) {
+    /* Maybe we could do a pointer comparison but we do not have any guarantee
+       that the metadata processor used the same pointers for consumed_md in the
+       callback. */
+    if (memcmp(GPR_SLICE_START_PTR(md->key->slice), calld->consumed_md[i].key,
+               GPR_SLICE_LENGTH(md->key->slice)) == 0 &&
+        memcmp(GPR_SLICE_START_PTR(md->value->slice),
+               calld->consumed_md[i].value,
+               GPR_SLICE_LENGTH(md->value->slice)) == 0) {
+      return NULL; /* Delete. */
+    }
+  }
+  return md;
+}
+
+static void on_md_processing_done(void *user_data,
+                                  const grpc_metadata *consumed_md,
+                                  size_t num_consumed_md, int success,
+                                  grpc_auth_context *result) {
+  grpc_call_element *elem = user_data;
+  call_data *calld = elem->call_data;
+
+  calld->success = success;
+  if (success) {
+    calld->consumed_md = consumed_md;
+    calld->num_consumed_md = num_consumed_md;
+    grpc_metadata_batch_filter(&calld->md_op->data.metadata, remove_consumed_md,
+                               elem);
+    GPR_ASSERT(calld->call_auth_context != NULL);
+    GRPC_AUTH_CONTEXT_UNREF(*calld->call_auth_context,
+                            "releasing old context.");
+    *calld->call_auth_context =
+        GRPC_AUTH_CONTEXT_REF(result, "refing new context.");
+  } else {
+    grpc_call_element_send_cancel(elem);
+  }
+
+  calld->on_done_recv->cb(calld->on_done_recv->cb_arg, success);
+}
+
+static void auth_on_recv(void *user_data, int success) {
+  grpc_call_element *elem = user_data;
+  call_data *calld = elem->call_data;
+  channel_data *chand = elem->channel_data;
+  if (success) {
+    size_t i;
+    size_t nops = calld->recv_ops->nops;
+    grpc_stream_op *ops = calld->recv_ops->ops;
+    for (i = 0; i < nops; i++) {
+      grpc_metadata_array md_array;
+      grpc_process_auth_metadata_func processor =
+          grpc_server_auth_context_get_process_metadata_func();
+      grpc_stream_op *op = &ops[i];
+      if (op->type != GRPC_OP_METADATA) continue;
+      calld->got_client_metadata = 1;
+      if (processor == NULL) continue;
+      calld->md_op = op;
+      md_array = metadata_batch_to_md_array(&op->data.metadata);
+      processor(&calld->ticket, chand->security_connector->auth_context,
+                md_array.metadata, md_array.count, on_md_processing_done, elem);
+      grpc_metadata_array_destroy(&md_array);
+      return;
+    }
+  }
+  calld->on_done_recv->cb(calld->on_done_recv->cb_arg, success);
+}
+
+static void set_recv_ops_md_callbacks(grpc_call_element *elem,
+                                      grpc_transport_stream_op *op) {
+  call_data *calld = elem->call_data;
+  channel_data *chand = elem->channel_data;
+
+  if (op->send_ops && !calld->sent_status && !calld->success) {
+    size_t i;
+    size_t nops = op->send_ops->nops;
+    grpc_stream_op *ops = op->send_ops->ops;
+    for (i = 0; i < nops; i++) {
+      grpc_stream_op *op = &ops[i];
+      if (op->type != GRPC_OP_METADATA) continue;
+      calld->sent_status = 1;
+      grpc_metadata_batch_add_head(
+          &op->data.metadata, &calld->status,
+          GRPC_MDELEM_REF(chand->status_auth_failure));
+      break;
+    }
+  }
+
+  if (op->recv_ops && !calld->got_client_metadata) {
+    /* substitute our callback for the higher callback */
+    calld->recv_ops = op->recv_ops;
+    calld->on_done_recv = op->on_done_recv;
+    op->on_done_recv = &calld->auth_on_recv;
+  }
+}
+
 /* Called either:
      - in response to an API call (or similar) from above, to send something
      - a network event (or similar) from below, to receive something
@@ -52,9 +193,7 @@ typedef struct channel_data {
    that is being sent or received. */
 static void auth_start_transport_op(grpc_call_element *elem,
                                     grpc_transport_stream_op *op) {
-  /* TODO(jboeuf): Get the metadata and get a new context from it. */
-
-  /* pass control down the stack */
+  set_recv_ops_md_callbacks(elem, op);
   grpc_call_next_op(elem, op);
 }
 
@@ -68,11 +207,18 @@ static void init_call_elem(grpc_call_element *elem,
   grpc_server_security_context *server_ctx = NULL;
 
   /* initialize members */
-  calld->unused = 0;
+  memset(calld, 0, sizeof(*calld));
+  grpc_iomgr_closure_init(&calld->auth_on_recv, auth_on_recv, elem);
+  calld->success = 1;
 
   GPR_ASSERT(initial_op && initial_op->context != NULL &&
              initial_op->context[GRPC_CONTEXT_SECURITY].value == NULL);
 
+  /* Get the pollset for the ticket. */
+  if (initial_op->bind_pollset) {
+    calld->ticket.pollset = initial_op->bind_pollset;
+  }
+
   /* Create a security context for the call and reference the auth context from
      the channel. */
   if (initial_op->context[GRPC_CONTEXT_SECURITY].value != NULL) {
@@ -85,10 +231,15 @@ static void init_call_elem(grpc_call_element *elem,
   initial_op->context[GRPC_CONTEXT_SECURITY].value = server_ctx;
   initial_op->context[GRPC_CONTEXT_SECURITY].destroy =
       grpc_server_security_context_destroy;
+  calld->call_auth_context = &server_ctx->auth_context;
+
+  /* Set the metadata callbacks. */
+  set_recv_ops_md_callbacks(elem, initial_op);
 }
 
 /* Destructor for call_data */
-static void destroy_call_elem(grpc_call_element *elem) {}
+static void destroy_call_elem(grpc_call_element *elem) {
+}
 
 /* Constructor for channel_data */
 static void init_channel_elem(grpc_channel_element *elem, grpc_channel *master,
@@ -109,6 +260,8 @@ static void init_channel_elem(grpc_channel_element *elem, grpc_channel *master,
   GPR_ASSERT(!sc->is_client_side);
   chand->security_connector =
       GRPC_SECURITY_CONNECTOR_REF(sc, "server_auth_filter");
+  chand->status_auth_failure =
+      grpc_mdelem_from_strings(mdctx, ":status", "401");
 }
 
 /* Destructor for channel data */
@@ -117,6 +270,7 @@ static void destroy_channel_elem(grpc_channel_element *elem) {
   channel_data *chand = elem->channel_data;
   GRPC_SECURITY_CONNECTOR_UNREF(chand->security_connector,
                                 "server_auth_filter");
+  GRPC_MDELEM_UNREF(chand->status_auth_failure);
 }
 
 const grpc_channel_filter grpc_server_auth_filter = {
diff --git a/src/core/transport/stream_op.h b/src/core/transport/stream_op.h
index 964d39d14f..7d3024da10 100644
--- a/src/core/transport/stream_op.h
+++ b/src/core/transport/stream_op.h
@@ -103,7 +103,7 @@ void grpc_metadata_batch_merge(grpc_metadata_batch *target,
                                grpc_metadata_batch *add);
 
 /** Add \a storage to the beginning of \a batch. storage->md is
-    assumed to be valid. 
+    assumed to be valid.
     \a storage is owned by the caller and must survive for the
     lifetime of batch. This usually means it should be around
     for the lifetime of the call. */