Optional[customOptional[unknownoptional, subject token for impersonation/delegation (who want to impersonate/delegate) in subject_token.
optional, token type for the impersonation/delegation (who want to impersonate/delegate). Usually it's urn:ietf:params:oauth:token-type:access_token
optional, name of the oauth client id on which this token will be used
required - urn:ietf:params:oauth:grant-type:token-exchange
optional type of requested token, default is urn:ietf:params:oauth:token-type:access_token
optional, list of resources approved to use by token, if applicable
optional (scopes of the token)
required - could be self signed JWT token
required, in case of jwt - urn:ietf:params:oauth:token-type:jwt
https://www.rfc-editor.org/rfc/rfc8693.html