A client device accesses content and performs actions at a remote application server via a user-agent application. The application server directs the user-agent application to a security verification system to retrieve and perform security tests. The security verification system receives information from the user-agent application describing characteristics of the user-agent application, and the security verification system selects a set of security tests to be performed by a security module executing in the user-agent application to verify that the user-agent application is accessing the application server consistent with the described user-agent application. The security verification system compares a set of test results with other user-agent applications and provides a token to the user-agent application to access the application server. The security module may also monitor and actions on the user-agent application to permit the security verification system to revise or revoke the token.