diff --git a/tests/authentication/AuthServerTest.php b/tests/authentication/AuthServerTest.php
index b6556f02..54c29ab7 100644
--- a/tests/authentication/AuthServerTest.php
+++ b/tests/authentication/AuthServerTest.php
@@ -806,6 +806,135 @@ class Authentication_Server_test extends PHPUnit_Framework_TestCase
         $this->assertEquals(time()+$a::getExpiresIn(), $v['expires']);
     }
 
+    /**
+     * @expectedException        OAuth2\Exception\ClientException
+     * @expectedExceptionCode    0
+     */
+    public function test_issueAccessToken_clientCredentialsGrant_missingClientId()
+    {
+        $a = $this->returnDefault();
+        $a->addGrantType(new OAuth2\Grant\ClientCredentials());
+
+        $request = new OAuth2\Request(array(), $_POST);
+        $a->setRequest($request);
+
+        $v = $a->issueAccessToken(array(
+            'grant_type'    =>  'client_credentials'
+        ));
+    }
+
+    /**
+     * @expectedException        OAuth2\Exception\ClientException
+     * @expectedExceptionCode    0
+     */
+    public function test_issueAccessToken_clientCredentialsGrant_missingClientCredentials()
+    {
+        $a = $this->returnDefault();
+        $a->addGrantType(new OAuth2\Grant\ClientCredentials());
+
+        $request = new OAuth2\Request(array(), $_POST);
+        $a->setRequest($request);
+
+        $v = $a->issueAccessToken(array(
+            'grant_type'    =>  'client_credentials',
+            'client_id' =>  1234
+        ));
+    }
+
+    /**
+     * @expectedException        OAuth2\Exception\ClientException
+     * @expectedExceptionCode    8
+     */
+    public function test_issueAccessToken_clientCredentialsGrant_badClient()
+    {
+        $this->client->shouldReceive('getClient')->andReturn(false);
+
+        $a = $this->returnDefault();
+        $a->addGrantType(new OAuth2\Grant\ClientCredentials());
+
+        $request = new OAuth2\Request(array(), $_POST);
+        $a->setRequest($request);
+
+        $v = $a->issueAccessToken(array(
+            'grant_type'    =>  'client_credentials',
+            'client_id' =>  1234,
+            'client_secret' =>  5678
+        ));
+    }
+
+    function test_issueAccessToken_clientCredentialsGrant_passedInput()
+    {
+        $this->client->shouldReceive('getClient')->andReturn(array(
+            'client_id' =>  1234,
+            'client_secret' =>  5678,
+            'redirect_uri'  =>  'http://foo/redirect',
+            'name'  =>  'Example Client'
+        ));
+
+        $this->client->shouldReceive('validateRefreshToken')->andReturn(1);
+
+        $this->session->shouldReceive('validateAuthCode')->andReturn(1);
+        $this->session->shouldReceive('createSession')->andReturn(1);
+        $this->session->shouldReceive('deleteSession')->andReturn(null);
+        $this->session->shouldReceive('updateRefreshToken')->andReturn(null);
+
+        $a = $this->returnDefault();
+        $a->addGrantType(new OAuth2\Grant\ClientCredentials());
+
+        $v = $a->issueAccessToken(array(
+            'grant_type'    =>  'client_credentials',
+            'client_id' =>  1234,
+            'client_secret' =>  5678
+        ));
+
+        $this->assertArrayHasKey('access_token', $v);
+        $this->assertArrayHasKey('token_type', $v);
+        $this->assertArrayHasKey('expires', $v);
+        $this->assertArrayHasKey('expires_in', $v);
+        $this->assertArrayHasKey('refresh_token', $v);
+
+        $this->assertEquals($a::getExpiresIn(), $v['expires_in']);
+        $this->assertEquals(time()+$a::getExpiresIn(), $v['expires']);
+    }
+
+    function test_issueAccessToken_clientCredentialsGrant()
+    {
+        $this->client->shouldReceive('getClient')->andReturn(array(
+            'client_id' =>  1234,
+            'client_secret' =>  5678,
+            'redirect_uri'  =>  'http://foo/redirect',
+            'name'  =>  'Example Client'
+        ));
+
+        $this->client->shouldReceive('validateRefreshToken')->andReturn(1);
+
+        $this->session->shouldReceive('validateAuthCode')->andReturn(1);
+        $this->session->shouldReceive('createSession')->andReturn(1);
+        $this->session->shouldReceive('deleteSession')->andReturn(null);
+        $this->session->shouldReceive('updateRefreshToken')->andReturn(null);
+
+        $a = $this->returnDefault();
+        $a->addGrantType(new OAuth2\Grant\ClientCredentials());
+
+        $_POST['grant_type'] = 'client_credentials';
+        $_POST['client_id'] = 1234;
+        $_POST['client_secret'] = 5678;
+
+        $request = new OAuth2\Request(array(), $_POST);
+        $a->setRequest($request);
+
+        $v = $a->issueAccessToken();
+
+        $this->assertArrayHasKey('access_token', $v);
+        $this->assertArrayHasKey('token_type', $v);
+        $this->assertArrayHasKey('expires', $v);
+        $this->assertArrayHasKey('expires_in', $v);
+        $this->assertArrayHasKey('refresh_token', $v);
+
+        $this->assertEquals($a::getExpiresIn(), $v['expires_in']);
+        $this->assertEquals(time()+$a::getExpiresIn(), $v['expires']);
+    }
+
     public function tearDown() {
         M::close();
     }