The type of authorization needed for this data source.
Values:
AUTHORIZATION_TYPE_UNSPECIFIED (0):
Type unspecified.
AUTHORIZATION_CODE (1):
Use OAuth 2 authorization codes that can be
exchanged for a refresh token on the backend.
GOOGLE_PLUS_AUTHORIZATION_CODE (2):
Return an authorization code for a given
Google+ page that can then be exchanged for a
refresh token on the backend.
FIRST_PARTY_OAUTH (3):
Use First Party OAuth.