Fragment

[btimby]

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [X] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Other, please describe:

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• [X] You consent that the copyright of your pull request source code belongs to Authlib's author.

This allows a parameter in_fragment to be passed into prepare_grant_uri(), when enabled, this will place OAuth parameters into the URL fragment rather than the query string. Further, it modifies add_params_to_uri() so that the original fragment is left unmolested (not made part of the parameters).

This is needed since I am using Vuejs for my frontend, and making API calls to perform OAuth2 authorization. I am using an authorization url such as:

http://localhost:8000/#/authorize

Without the in_fragment param, you would receive the url:

http://localhost:8000/?response_type=...#/authorize

And without preserving the fragment, you would get:

http://localhost:8000/#/authorize?%2Fauthorize&response_type=...

With these changes, the URL is correctly:

http://localhost:8000/#/authorize?response_type=...