Preventing Cross-Site Request Forgery and/or Session Fixation with the state parameter.

[jankapunkt]

The state parameter is a random value, generated by the client. The parameter will then always be included in subsequent communication with the AS. It allows the client to validate that the access token it receives corresponds to the preceeding authorization request. Without this parameter, an attacker could inject his own access token, and therefore grant access to resources that the attacker controls. The end-user would then e.g. publish his data on the attacker's account. So for the penetration test, you should check whether the library properly validates the state parameter, or if you can alter the value.