You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: oidcadaptor.go
    path of file: ./repos/easegress/pkg/filters/oidcadaptor
    
    the code of the file until where you have to start completion: /*
 * Copyright (c) 2017, The Easegress Authors
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language gover
    
func (o *OIDCAdaptor) validateIDToken(idJwtToken string) (*jwt.Token, error) {
	parseJwtToken, err := jwt.Parse(idJwtToken, func(token *jwt.Token) (interface{}, error) {
		alg := token.Method.Alg()
		// If the JWT alg Header Parameter uses a MAC based algorithm such as HS256, HS384, or HS512,
		// the octets of the UTF-8 representation of the client_secret corresponding to the client_id
		// contained in the aud (audience) Claim are used as the key to validate the signature
		if strings.HasPrefix(strings.ToLower(alg), "hs") {
			return []byte(o.spec.ClientSecret), nil
		}
		return o.jwks.Keyfunc(token)
	})
	if err != nil {
		return nil, err
	}
	if !parseJwtToken.Valid {
		return nil, fmt.Errorf("invalid id token")
	}
	return parseJwtToken, nil
}