Add support for screen_hint=signup param

[bbean86]

Changes

This adds support for the Hosted Login screen_hint=signup parameter. I discovered this issue while implementing Auth0 in a new Rails 6 app using Hosted Login. I noticed others had the same experience, so I thought I'd share my solution.

References

#87

Testing

This can be tested by adding the screen_hint=signup query parameter to the /auth/auth0 request. You should be able to observe the screen_hint parameter being sent to the Auth0 /authorize endpoint.

• This change adds unit test coverage
• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors
• All code quality tools/guidelines in the CONTRIBUTING documentation have been run/followed

[lbalmaceda]

@bbean86 something to notice though is that this introduced param will only work with the "New Universal Login Experience". "Classic Experience" didn't support this, last time I checked.
Can you add a note somewhere in the readme for these additional params? (all of possible, they are not many) and for this one in particular, warn that it's only available with the new experience. Thanks

[lbalmaceda]

what is this line doing, allowing these keys to be taken from the URL query and setting them on the /authorize call?

[lbalmaceda]

There's a existing test for checking that on a "normal authorize call" (without extra args) these keys are not part of the query. Let's add this one there, and also the ones that are missing from previous changes.

The test is on these lines:

omniauth-auth0/spec/omniauth/strategies/auth0_spec.rb

Lines 84 to 86 in 894d4e2

	expect(redirect_url).not_to have_query('auth0Client')
	expect(redirect_url).not_to have_query('connection')
	expect(redirect_url).not_to have_query('prompt')

Let's add a line for testing that the following keys are NOT in the query:

• connection_scope
• screen_hint

[lbalmaceda]

👋 @bbean86 friendly check-in, are you still interested in these changes?

[bbean86]

@lbalmaceda apologies, I will circle back to these updates this weekend. This update is still relevant to my needs.

[lbalmaceda]

@bbean86 thanks for the update! My team is tracking the pending release internally under SDK-1966.