'Retrieve a user\'s access/secret pair by the access key.
Grab the full access/secret pair for a given access key.
:param user_id: id of user
:param credential_id: access key for credentials
:returns: credential: dict of ec2 credential'

def get_credential(self, user_id, credential_id):

    self.identity_api.get_user(user_id)
    return {'credential': self._get_credentials(credential_id)}
