The main token type of OAuth 2 is Bearer tokens and that is what OAuthLib currently supports. Other tokens, such as SAML and MAC can easily be added.

The purpose of a token is to authorize access to protected resources to a client (i.e. your G+ feed).

The spec requires a token_type in access token responses, but some providers, notably Facebook, do not provide this information. Per the robustness principle, we default to the Bearer token type if this value is missing. You can force a MissingTokenTypeError exception instead, by setting OAUTHLIB_STRICT_TOKEN_TYPE in the environment.