Support OAuth flow for Connect accounts

[robz-stripe]

r? @remi-stripe
cc @stripe/api-libraries

Fixes #422

[robz-stripe]

Tested this via the steps at https://stripe.com/docs/connect/standard-accounts and the access code redeemed correctly for a token.

[ob-stripe]

Hey @robz-stripe, thanks for taking a stab at this!

This looks like a great start. Before we merge this however, I think we need some additional features for bring this to parity with our other libraries:

• a utility authorizeURL method for creating the https://connect.stripe.com/oauth/authorize?... redirection URL (doc)
  • this method should have an option for Express accounts, to change the resulting URL to https://connect.stripe.com/express/oauth/authorize?...
• support for deauthorizing accounts via the /oauth/deauthorize endpoint (doc)

If you haven't already, I recommend you take a look at the implementations in other languages, particularly stripe-ruby's: https://github.com/stripe/stripe-ruby/blob/master/lib/stripe/oauth.rb. (If I'm not mistaken, stripe-ruby is the only one that supports Express accounts right now.)

Also, very minor nit, but would you mind changing the capitalization from Oauth to OAuth?

[robz-stripe]

r? @ob-stripe

This implements authorizeUrl and deauthorize as well, now.

[robz-stripe]

Making a note here to update https://github.com/stripe/stripe-node/wiki/Using-Stripe-Connect-with-node.js once the interface is finalized.

[ob-stripe]

Great job @robz-stripe, this looks great. I've left a couple of comments, but nothing I feel too strongly about.

@rattrayalex-stripe @jlomas-stripe Would one of you Node-fu masters mind taking a look at this?

[remi-stripe]

r? @rattrayalex-stripe as our node expert

[rattrayalex-stripe]

Nice!

Few nits, would be nice to see the tests get a bit more granular but not bad as they are; fine to leave if you prefer as-is.

[robz-stripe]

Cleaned up the tests to be more granular and simpler to grok. Let me know what you think!

[rattrayalex-stripe]

✨
Awesome! Thanks @robz-stripe !

[samheutmaker]

Thanks @robz-stripe!

[Nisthar]

@robz-stripe is there an example to do oauth with this lib?

[noah-witt]

Any way to get this documented in the API?

[remi-stripe]

@Nisthar You can find examples in the repo here: https://github.com/stripe/stripe-node/blob/master/test/resources/OAuth.spec.js

@noah-witt Yes we're working on adding examples to our docs!