Add support for kid header in call to Oauth2 servers

[bscholtes1A]

Bug Report

Describe the Bug

As of today, Oauth2AssertionDecorator does not provide the capability to encode the optional kid header in the access token request to Oauth2 server.

Expected Behavior

We should be able to specify a kid: https://www.rfc-editor.org/rfc/rfc7515#page-11

Observed Behavior

kid header is not supported.

Steps to Reproduce

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1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Context Information

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• Used version [e.g. EDC v1.0.0]
• OS: [e.g. iOS, Windows]
• ...

Detailed Description

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Possible Implementation

You already know the root cause of the erroneous state and how to fix it? Feel free to share your thoughts.