Redirect to uri even if --skip-provider-button

[leon-barrett]

The normal behavior is that if a user is going to page
https://hostname/x but is not authenticated, they are sent to login and
then redirected back to https://hostname/x.

I discovered that if the flag --skip-provider-button is given, then
after login the user ends up at https://hostname/.

I believe this to be a bug. That behavior seems to happen because the
current URI is only extracted when redirecting to the sign-in page form,
not when the OAuth flow is started, so if that form is skipped, the
current URL is lost. Therefore, I made a change to extract the current
page to send into the OAuth flow.

This change fixes that bug and adds a test.

[leon-barrett]

While the tests failed, they seemed to fail on dependencies (none of which I touched).

https://travis-ci.org/bitly/oauth2_proxy/jobs/462032033#L588

ensure Solve(): No versions of gopkg.in/fsnotify.v1 met constraints:

https://travis-ci.org/bitly/oauth2_proxy/jobs/462032032#L570

../../../golang.org/x/oauth2/google/default.go:38: syntax error: unexpected = in type declaration

I can investigate what's needed to update those dependencies, but I'd naively expect that you'd have more luck :)

[leon-barrett]

Ah, it looks like #610 is at least a partial fix.

[ploxiln]

this repo is unmaintained, see #628 (comment)

[leon-barrett]

Thanks. I'll just close this down.