populateRequest

Internal function to populate an OIDC authorization request with the necessary parameters.

This function handles both standard OAuth2 authorization requests and PAR (Pushed Authorization Request):

Standard Flow:

• Builds authorization URL with all parameters in the query string

• Suitable for most OAuth2/OIDC implementations

PAR Flow (RFC 9126):

• First pushes authorization parameters to the PAR endpoint via POST

• Receives a request_uri that references the pushed parameters

• Uses the request_uri in the actual authorization request

• Provides better security and reduces URL length

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