Function nginx::SSL_CTX_set_srp_username_callback

pub unsafe extern "C" fn SSL_CTX_set_srp_username_callback(
    ctx: *mut SSL_CTX, 
    cb: Option<unsafe extern "C" fn(arg1: *mut SSL, arg2: *mut c_int, arg3: *mut c_void) -> c_int>
) -> c_int