oauth2: add device flow support

[centimitr]

draft-ietf-oauth-device-flow
https://tools.ietf.org/html/draft-ietf-oauth-device-flow-13

Draft: device flow is still a draft, but it is a very handy flow for many practical cases.

This pr includes an early stage implementation of the device flow, according to the draft, and it works with Azure AD. I am going to add tests and doing some refactor, like renaming AuthCodeOption with type alias etc. I am looking for the time it can be merged as a standard.

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[centimitr]

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This PR (HEAD: 7cf8880) has been imported to Gerrit for code review.

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[mihaiav]

any chance to have this merged? "device flow" has become quite common.

[mihaiav]

@devbycm I believe you should have a select on <- ctx.Done() inside that loop to check of context cancelation.

[ajohanssonwalder]

I don't believe the code parameter is required in this request - see rfc8628#section-3.4

[gopherbot]

Message from Go Bot:

Patch Set 1:

Congratulations on opening your first change. Thank you for your contribution!

Next steps:
Within the next week or so, a maintainer will review your change and provide
feedback. See https://golang.org/doc/contribute.html#review for more info and
tips to get your patch through code review.

Most changes in the Go project go through a few rounds of revision. This can be
surprising to people new to the project. The careful, iterative review process
is our way of helping mentor contributors and ensuring that their contributions
have a lasting impact.

During May-July and Nov-Jan the Go project is in a code freeze, during which
little code gets reviewed or merged. If a reviewer responds with a comment like
R=go1.11, it means that this CL will be reviewed as part of the next development
cycle. See https://golang.org/s/release for more details.

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Please don’t reply on this GitHub thread. Visit golang.org/cl/156537.
After addressing review feedback, remember to publish your drafts!

[mniak]

Hey, please fix the conflicting file. This feature will be so useful!

[GreyXor]

@centimitr Hello, thanks for this PR. Apart from the conflict, is there anything else missing? any chance to have this merged?

[devster31]

@centimitr these lines are creating a merge conflict, you'd just need to slightly change this bit to match the new version of the file and it'd be a straight merge.

[Morishiri]

@centimitr are you able to fix the merge conflicts and get this merged?
If no, is it ok to take it over and get this delivered?

[hickford]

Implemented in e3fb0fb