JWT and JWE compatible Self-Encoded Access Tokens

Feature
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To ensure compatibility and transparency, the self encoded access tokens should be structured based on an open standard, such as [JWT][JWT]. Since private data is needed for several potential extensions, encryption with [JWE][JWE] should also be possible.

This should ultimately lead to better interoperability with clients and might improve debugging as supporting tools etc. are developed independently.

Tracking pull request
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[JWT]: https://tools.ietf.org/html/rfc7519
[JWE]: https://tools.ietf.org/html/rfc7516

The issue proposes implementing JWT and JWE standards for self-encoded access tokens. Start by examining the current token handling code in the codebase, likely in modules related to token generation and validation. Review the RFCs linked (RFC 7519 for JWT, RFC 7516 for JWE) to understand the standards. Look for existing tests for tokens to see the expected behavior. 'Done' means tokens are generated and validated according to these standards, with encryption support.

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