forgejo -- multiple vulnerabilities

Problem Description:

• Forgejo generates a token which is used to authenticate web endpoints that are only meant to be used internally, for instance when the SSH daemon is used to push a commit with Git. The verification of this token was not done in constant time and was susceptible to timing attacks. A pre-condition for such an attack is the precise measurements of the time for each operation. Since it requires observing the timing of network operations, the issue is mitigated when a Forgejo instance is accessed over the internet because the ISP introduce unpredictable random delays.
• Because of a missing permission check, the branch used to propose a pull request to a repository can always be deleted by the user performing the merge. It was fixed so that such a deletion is only allowed if the user performing the merge has write permission to the repository from which the pull request was made.