<Issue Description> Spring Security OAuth versions 2.5.x prior to 2.5.2 and older unsupported versions are susceptible to a Denial-of-Service (DoS) attack via the initiation of the Authorization Request in an OAuth 2.0 Client application. A malicious user or attacker can send multiple requests initiating the Authorization Request for the Authorization Code Grant which has the potential of exhausting system resources using a single session. This vulnerability exposes OAuth 2.0 Client applications only.