A Certificate Signing Request contains the public key that the certificate authority will place into the issued certificate. The SSLFOR CSR + Key Matcher verifies the CSR signature and compares its RSA public components with the supplied private key.
Use this before submitting a CSR to a certificate authority or when confirming that a saved private key is the one originally used to create the request. A mismatch means a certificate issued from that CSR will not work with the supplied private key.
The CSR and private key are processed locally in the browser.