feature: Discord OAuth2 Provider

[mgkbadola]

Added login support for Discord. If this is approved and merged, I would like to add it's its support to Remark42 (love that service).

A request: Since I am currently participating in Hacktoberfest, if this PR is to be merged, kindly add the label hacktoberfest-accepted to it. Many thanks!

[umputun]

Thanks. I don't see anything wrong with this PR. @paskal - can you please take a look and double-check?

[umputun]

@mgkbadola - pls fix the linter issue, look like a public method without a comment

[mgkbadola]

@mgkbadola - pls fix the linter issue, look like a public method without a comment

on it 👍🏽 done

[paskal]

Thanks, will check and test shortly. Could you please add it to the v2 as well?

[coveralls]

Pull Request Test Coverage Report for Build 11195676729

Details

• 21 of 23 (91.3%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 83.344%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
provider/providers.go	19	21	90.48%

Totals
Change from base Build 11078013402:	0.06%
Covered Lines:	2612
Relevant Lines:	3134

---

💛 - Coveralls

[paskal]

Overall good and works, but you need to drop email retrieval as the rest of the providers don't request any information not required for the unique user identification, and email is an extra information.

You can use umputun/remark42@53e9c98 as a reference when preparing changes for Remark42, just please don't forget to add discord.svg file which is not present in the commit: I've tested the auth with facebook icon.

[paskal]

According to the rules:

For your pull requests to be accepted, the request must either be merged, have the Hacktoberfest-accepted label, or have an overall approving review on GitHub.

I think this PR will be counted once merged.

[badolamgk]

Hey/Privyet @paskal
I have done the required changes. Thanks for reviewing and providing reference for Remark42.

[badolamgk]

Hey @umputun

Let me know if there are any other changes required on my end. Cheers.

[badolamgk]

For the below command,

go test -timeout=60s -v -race -p 1 -covermode=atomic ./...

Test cases passing on my workstation, attaching logs here.