Add Spotify Provider

[romch007]

Proposed changes

I added a Spotify driver. Informations about Spotify OAuth : https://developer.spotify.com/documentation/general/guides/authorization-guide/

Types of changes

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• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• [x] Lint and unit tests pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added necessary documentation (if appropriate)

Further comments

[romch007]

Small question, I find it strange the port is hard-coded, given that the PORT environment variable is used elsewhere, especially for callbackUrls

https://github.com/adonisjs/ally/blob/3891b85d1b362c7a16cd26c85a3ca02d470964d5/examples/app.ts#L14

[thetutlage]

Small question, I find it strange the port is hard-coded, given that the PORT environment variable is used elsewhere, especially for callbackUrls

Seems like a mistake, feel free to fix it in the same PR

[thetutlage]

Thanks a ton for putting in the work :)