AppendKeyPair loads the given TLS key pair and appends it to tlsConfig.Certificates.

Read in a keypair where the key is password protected.

Print a password prompt on the terminal and collect a password.

Determine if a string element is in a string array.

Determine if PEM file is encrypted.

ListenAndServeTLS acts identically to http.ListenAndServeTLS, except that it expects TLS configuration.

NewTLSConfig returns an initialized TLS configuration suitable for client authentication.

Read a PEM file and ask for a password to decrypt it if needed.

Verify that the OU of the presented client certificate matches the list of Valid OUs.

TODO: make this testable?.