Here is some early code with specific features, written before the envisioning phase of OpenSSO project. It is here because of historical purposes.

This patch works for Mantis bug tracker (http://www.mantisbt.org). Tested with versions 1.0 to 1.0.6. Functionality includes:
• Automatic user registration in Mantis with info from the certificate. If you need to differentiate access to the projects within Mantis to specific users, make all projects private and add the new registered users only to their projects
• If there is already user in the system, the agent checks emails to assign certificate to current user. Warning! This requires being able to trust certificate issuer!
• Checks user table in Mantis for possible logical corruption in data