code: func (a *AuthWithRoles) AuthenticateSSHUser(req AuthenticateSSHRequest) (*SSHLoginResponse, error) {
  	// authentication request has it's own authentication, however this limits the requests
  	// types to proxies to make it harder to break
  	if !a.hasBuiltinRole(string(teleport.RoleProxy)) {
  		return nil, trace.AccessDenied("this request can be only executed by a proxy")
  	}
  	return a.authServer.AuthenticateSSHUser(req)
  }
docs: // AuthenticateSSHUser authenticates SSH console user, creates and  returns a pair of signed TLS and SSH
  // short lived certificates as a result