Support for oauth2 with "client_credentials" grant type

Release/include/cpprest/details/http_constants.dat

@@ -190,6 +190,7 @@ DAT(expires_in,                     "expires_in")
 DAT(grant_type,                     "grant_type")
 DAT(redirect_uri,                   "redirect_uri")
 DAT(refresh_token,                  "refresh_token")
+DAT(client_credentials,             "client_credentials")
 DAT(response_type,                  "response_type")
 DAT(scope,                          "scope")
 DAT(state,                          "state")

Release/include/cpprest/oauth2.h

@@ -284,6 +284,21 @@ class oauth2_config
         return _request_token(ub);
     }
 
+    /// <summary>
+    /// Fetches an access token from the token endpoint using client credentials grant type.
+    /// The task creates an HTTP request to the token_endpoint() using
+    /// client authentication as the authorization grant.
+    /// See: http://tools.ietf.org/html/rfc6749#section-4.4
+    /// </summary>
+    /// <returns>Task that fetches token(s) using client credentials.</returns>
+    pplx::task<void> token_from_client_credentials()
+    {
+        uri_builder ub;
+        ub.append_query(
+            details::oauth2_strings::grant_type, details::oauth2_strings::client_credentials, false);
+        return _request_token(ub);
+    }
+
     /// <summary>
     /// Returns enabled state of the configuration.
     /// The oauth2_handler will perform OAuth 2.0 authentication only if

Release/tests/functional/http/client/oauth2_tests.cpp

@@ -291,6 +291,74 @@ SUITE(oauth2_tests)
         VERIFY_ARE_EQUAL(U("done"), m_oauth2_config.token().access_token());
     }
 
+    TEST_FIXTURE(oauth2_test_setup, oauth2_token_from_client_credentials)
+    {
+        VERIFY_IS_FALSE(m_oauth2_config.is_enabled());
+
+        m_oauth2_config.set_user_agent(U("test_user_agent"));
+
+        // Fetch using HTTP Basic authentication.
+        {
+            m_scoped.server()->next_request().then([](test_request* request) {
+                VERIFY_ARE_EQUAL(request->m_method, methods::POST);
+
+                VERIFY_IS_TRUE(is_application_x_www_form_urlencoded(request));
+
+                VERIFY_ARE_EQUAL(
+                    U("Basic MTIzQUJDOjQ1NkRFRg=="),
+                    request->m_headers[header_names::authorization]);
+
+                VERIFY_ARE_EQUAL(
+                    to_body_data(U("grant_type=client_credentials")),
+                    request->m_body);
+
+                VERIFY_ARE_EQUAL(
+                    U("test_user_agent"),
+                    get_request_user_agent(request));
+
+                std::map<utility::string_t, utility::string_t> headers;
+                headers[header_names::content_type] = mime_types::application_json;
+                request->reply(
+                    status_codes::OK, U(""), headers, "{\"access_token\":\"xyzzy123\",\"token_type\":\"bearer\"}");
+            });
+
+            m_oauth2_config.token_from_client_credentials().wait();
+            VERIFY_ARE_EQUAL(U("xyzzy123"), m_oauth2_config.token().access_token());
+            VERIFY_IS_TRUE(m_oauth2_config.is_enabled());
+        }
+
+        // Fetch using client key & secret in request body (x-www-form-urlencoded).
+        {
+            m_scoped.server()->next_request().then([](test_request* request) {
+                VERIFY_IS_TRUE(is_application_x_www_form_urlencoded(request));
+
+                VERIFY_ARE_EQUAL(U(""), request->m_headers[header_names::authorization]);
+
+                VERIFY_ARE_EQUAL(
+                    to_body_data(U("grant_type=client_credentials&client_id=123ABC&client_secret=456DEF")),
+                    request->m_body);
+
+                VERIFY_ARE_EQUAL(U("test_user_agent"), get_request_user_agent(request));
+
+                std::map<utility::string_t, utility::string_t> headers;
+                headers[header_names::content_type] = mime_types::application_json;
+                request->reply(
+                    status_codes::OK, U(""), headers, "{\"access_token\":\"xyzzy123\",\"token_type\":\"bearer\"}");
+            });
+
+            m_oauth2_config.set_token(oauth2_token()); // Clear token.
+            VERIFY_IS_FALSE(m_oauth2_config.is_enabled());
+
+            m_oauth2_config.set_http_basic_auth(false);
+            m_oauth2_config.token_from_client_credentials().wait();
+
+            VERIFY_ARE_EQUAL(
+                U("xyzzy123"),
+                m_oauth2_config.token().access_token());
+            VERIFY_IS_TRUE(m_oauth2_config.is_enabled());
+        }
+    }
+
     TEST_FIXTURE(oauth2_test_setup, oauth2_bearer_token)
     {
         m_oauth2_config.set_token(oauth2_token(U("12345678")));