title: Not able to create google credential for app engine project
body: <p>I am trying to create application default credentials for my app engine project for accessing google APIs. I am developing in eclipse IDE and I have defined the environment variable:GOOGLE_APPLICATION_CREDENTIALS to point to the json key file downloaded to my computer. But, I am gettin following exception:</p>
  
  <blockquote>
    <p>java.io.IOException: Application Default Credentials failed to create
    the Google App Engine service account credentials class
    com.google.api.client.googleapis.extensions.appengine.auth.oauth2.AppIdentityCredential$AppEngineCredentialWrapper.
    Check that the component 'google-api-client-appengine' is deployed.</p>
  </blockquote>
  
  <p><strong>Stacktrace:</strong></p>
  
  <blockquote>
    <p>Application Default Credentials failed to create the Google App Engine
    service account credentials class<br>
    com.google.api.client.googleapis.extensions.appengine.auth.oauth2.AppIdentityCredential$AppEngineCredentialWrapper.
    Check that the component 'google-api-client-appengine' is deployed.
    java.io.IOException: Application Default Credentials failed to create
    the Google App Engine service account credentials class
    com.google.api.client.googleapis.extensions.appengine.auth.oauth2.AppIdentityCredential$AppEngineCredentialWrapper.
    Check that the component 'google-api-client-appengine' is deployed.
      at
    com.google.api.client.googleapis.auth.oauth2.DefaultCredentialProvider.tryGetAppEngineCredential(DefaultCredentialProvider.java:282)
      at
    com.google.api.client.googleapis.auth.oauth2.DefaultCredentialProvider.getDefaultCredentialUnsynchronized(DefaultCredentialProvider.java:161)
      at
    com.google.api.client.googleapis.auth.oauth2.DefaultCredentialProvider.getDefaultCredential(DefaultCredentialProvider.java:88)
      at
    com.google.api.client.googleapis.auth.oauth2.GoogleCredential.getApplicationDefault(GoogleCredential.java:213)
      at
    com.google.api.client.googleapis.auth.oauth2.GoogleCredential.getApplicationDefault(GoogleCredential.java:191)</p>
  </blockquote>