Support token_uri and revoke_uri in ServiceAccountCredentials

[thobrla]

This change adds support for custom authorization token
and revocation URIs in the various ServiceAccountCredentials
factory methods.

It also makes the factory method from_p12_keyfile_contents
public for use by clients who have already loaded the file.

[nathanielmanistaatgoogle]

Who wants to lead review? @dhermes? @jonparrott? Should we be reticent about promoting ServiceAccountCredentials._from_p12_keyfile_contents to public visibility?

[dhermes]

@nathanielmanistaatgoogle You get the prize (as the official official maintainer).

No need to make _from_p12_keyfile_contents public though, maybe @thobrla has a reason I haven't though of?

[thobrla]

The argument for publicizing from_p12_keyfile_contents is that currently if I have already read the file (say for the purposes of determining whether it's a JSON file or not), there is no need for oauth2client to re-open the file

[thobrla]

ping @nathanielmanistaatgoogle (this request blocks a few others in my pipeline)

[dhermes]

RE:

The argument for publicizing from_p12_keyfile_contents is that currently if I have already read the file (say for the purposes of determining whether it's a JSON file or not), there is no need for oauth2client to re-open the file

A user can just use from_p12_keyfile_buffer and put the already read contents in a StringIO buffer.

[thobrla]

A user can just use from_p12_keyfile_buffer and put the already read contents in a StringIO buffer.

Done.

[thobrla]

FYI, I need to amend this to take token/revoke URIs from a JSON key file to fix #513. The new behavior will be:

1. If the user specifies a token/revoke URI in arguments, use that.
2. Else if the key file specifies token/revoke URI, use that.
3. Else use the Google defaults.

[thobrla]

Amendments complete, this now fixes #513

[thobrla]

Ping - this should be ready to go.

[theacodes]

@nathanielmanistaatgoogle is out on vacation.

@thobrla I'd still like to see the comments around the revoke_uri parameter addressed. Please completely document or cross-ref that argument.

After that, this change LGTM. However, I'd like to have @dhermes take a look before I merge if he has the time.

[thobrla]

PTAL

Made revoke_uri comments more verbose.

[theacodes]

Two more comments. If @dhermes doesn't object by EOD today, I'll merge once those two comments are addressed.

[dhermes]

I don't have much bandwidth but this looks mostly OK.

[theacodes]

Thanks, @dhermes