Annoying invalid credentials with oauth 2.0 google + api

Have you tried one of the Google API clients? There are starter applications you can use to get the ball rolling.

https://developers.google.com/+/downloads

Here is a solution using PHP's pecl oauth extension. The will sign the request the way you have defined it. In this case in a config file json object that was imported into the script.

        $oauth = new OAuth($this->config->consumer_key, $this->config->consumer_secret, $this->config->signature_method, $this->config->auth_type);
        $oauth->setVersion($this->config->version);
        $oauth->setToken($accessToken->oauth_token, $accessToken->oauth_token_secret);

        $params = array(
            'fields' => 'displayName,emails,id,image,name',
            'pp' => 1
        );

        $oauth->fetch('https://www.googleapis.com/plus/v1/people/me', $params, OAUTH_HTTP_METHOD_GET);

        // extract response
        $json = Zend_Json::decode($oauth->getLastResponse(), Zend_Json::TYPE_OBJECT);

You shouldn't share an unaltered access token - someone can use that to impersonate you (really for whomever it was granted).

It's also better to pass the Auth token as a header, like:

curl -H "Authorization: OAuth ya29.xyzxyz" "https://www.googleapis.com/plus/v1/people/me"

Not sure if that's essential but your error message seems to indicate an auth error in the header so you may be providing an Authorization header which doesn't match the one you need.