'Constructor for AssertionFlowCredentials.
Args:
assertion_type: string, assertion type that will be declared to the auth
server
user_agent: string, The HTTP User-Agent to provide for this application.
token_uri: string, URI for token endpoint. For convenience
defaults to Google\'s endpoints but any OAuth 2.0 provider can be used.
revoke_uri: string, URI for revoke endpoint.'

@util.positional(2)
def __init__(self, assertion_type, user_agent=None, token_uri=GOOGLE_TOKEN_URI, revoke_uri=GOOGLE_REVOKE_URI, **unused_kwargs):

    super(AssertionCredentials, self).__init__(None, None, None, None, None, token_uri, user_agent, revoke_uri=revoke_uri)
    self.assertion_type = assertion_type
