CTX_set_srp_username_callback() function sets the server side callback that is invoked when an SRP username is found in a ClientHello. The callback parameters are the SSL connection <b>s</b>, a writable error flag <b>ad</b> and the extra argument <b>arg</b> set by SSL_CTX_set_srp_cb_arg(). This callback should setup the server for the key exchange by calling SSL_set_srp_server_param() with the appropriate parameters for the received username. The username can be obtained by calling SSL_get_srp_username(). S