Per https://datatracker.ietf.org/doc/html/rfc7521#section-4.1,
client_id parameter, although optional, can still be passed
when using assertions as authorization grants. Adding a way to pass
that id to refresh token body.

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

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

Does this PR introduce a breaking change? (check one)

• Yes
• No

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