OAuth support

[lmagyar]

Proposed Changes

Continuation of / supersedes #1260.

Plus fixed some things:

• handle race condition in _check_api_key()
• handle token expiration
• handle token invalidation
• fix argument validation condition
• fix attribute initialization
• remove magic constant
• add tests

Plus added possibility to automatically store and retrieve the received OAuth token.

Related Issues

closes #1260 #1140

[clayrosenthal]

Nice work! This seems like all great improvements over my first step. I don't have any faith at this point that @frenck even looks at this repo, but we can dream

[frenck]

Nice work! This seems like all great improvements over my first step. I don't have any faith at this point that @frenck even looks at this repo, but we can dream

I do.