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state (optional): The state parameter provided by the client, if any.
session_state: A unique value that identifies the current user session.
In case of an error condition, depending on the error type, an error message will be displayed either directly to the end user (if there is a problem with the client ID or redirect URI), or it will be provided as an error parameter in the redirect URI to the client. For instance, if the end user does not give his or her consent, an "access_denied" error is returned to the client. See the specification section 4.1.2.1 for details.
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