Non-standard token response

[sagikazarmark]

I honestly don't know why anyone would ever do this, but some providers think it's a good idea to serve tokens in an arbitrary format.

Currently it requires rewriting a considerable amount of code to support these custom responses. It would be nice if it would be easier to hook into the token parsing flow.

I understand that supporting implementations deviating from standards is an endless debate (khm...HTTP), so I understand if this never lands in the library, but I thought I'd start a discussion at least.

I'd be happy to work on this if the maintainers decide that they would allow to land something like this.

I've found a similar issue describing a very specific case here: #197

[andig]

@sagikazarmark I support this, see #484 for a specific, imho wide-spread use case.

I understand that supporting implementations deviating from standards is an endless debate (khm...HTTP), so I understand if this never lands in the library, but I thought I'd start a discussion at least.

I would suggest to make the token unmarshaling a configurable process, maybe per refreshable token source. See https://github.com/evcc-io/evcc/blob/master/util/oauth/tokensource.go for a hacked-together version that will also support custom token refresh processes.

I would also like to work on this. Unfortunately it seems that there is currently little feedback on issues from outside Google, maybe @bradfitz could help?