Load user email in LinkedIn provider

[JakubSzajna]

As per https://github.com/Sorcery/sorcery/blob/master/lib/generators/sorcery/templates/migration/core.rb user email is a mandatory field in the DB. Thus, the recent fix for LinkedIn provider will produce an error when you try to register a new profile with it.

This fix loads user email from the additional endpoint in LinkedIn API v2 following this description: https://docs.microsoft.com/en-us/linkedin/consumer/integrations/self-serve/sign-in-with-linkedin?context=linkedin/consumer/context#retrieving-member-email-address

[chhlga]

Do we have enough specs to test this case?

[joshbuker]

@chhga unfortunately we don't have reliable specs for any of the OAuth providers. I don't know that it's worth the dev-time to develop it however, as the plan is to switch to Omniauth at some point. That being said, I wouldn't be opposed if someone wanted to put the time into creating specs. We can definitely use more coverage.

[joshbuker]

I realized that this doesn't conditionally check for the r_emailaddress scope, and will always hit the email url. This could have unintended consequences for apps that only use r_liteprofile.

[joshbuker]

I'm tempted to change the comment inside the initializer, but the code itself looks good to go.

I'll add the changelog and tweak the wording a little bit in the initializer before merging.

[joshbuker]

Thank you @JakubSzajna for your work on this! Merging.