Which client authentication mechanism can help a server verify that a connection request is originating from a pre-authorized endpoint?

The client authentication mechanism that allows a server to verify that a connection request is originating from a pre-authorized endpoint is network access control (NAC) authentication. NAC works by implementing security policies that define which devices can connect to the network. It checks the compliance of devices against pre-set criteria, such as operating system versions, antivirus status, and security patches. Only devices that meet these criteria are granted access, ensuring that the connection request is genuinely from an approved endpoint.

NAC systems typically utilize various methods to enforce these policies and manage device access, including checking device health and identity verification. As a result, NAC plays a crucial role in maintaining network security by confirming that requests come from authenticated sources before allowing access, thereby protecting the network from unauthorized devices.

Other authentication methods, while important, don't provide the same level of endpoint verification. For instance, SSH keys facilitate secure access to servers but do not evaluate the compliance state of the device initiating the connection. Similarly, digital signatures and code signing are primarily used to verify the authenticity and integrity of data or software rather than to authenticate the device itself when accessing a network. Therefore, NAC is the most suitable choice for ensuring that connection requests come from pre-authorized endpoints.