Update GitHubProvider to send token via header

[stringbean]

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• Have you added tests for any changed functionality?

Purpose

Updates GitHubProvider to send the OAuth2 token via an authorization header instead of a query param. This is needed as GitHub have deprecated the query param mechanism and are notifying API users periodically about this.

Note: this might be a breaking change for any users that have overridden the GitHub URL.

Background Context

Based the changes on the Dropbox provider which also sends via a header.

References

• GitHub Developer blog post discussing the deprecation.

[stringbean]

I'll also raise a PR against minutemen/silhouette with the same changes.

[coveralls]

Coverage increased (+0.08%) to 95.909% when pulling 8f27411 on stringbean:github-oauth-header into 1d6defb on mohiva:master.

[coveralls]

Coverage decreased (-0.07%) to 95.763% when pulling 8f27411 on stringbean:github-oauth-header into 1d6defb on mohiva:master.

[coveralls]

Coverage decreased (-0.07%) to 95.763% when pulling 8f27411 on stringbean:github-oauth-header into 1d6defb on mohiva:master.

[akkie]

@stringbean Many thanks 👍 . Will be released with the next Silhouette version targeting Play 2.8