Google Maps Tracks API 401 Invalid Credentials - node.js

Question

I do have checked validity of my access_token at https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=mytoken
which is replying as follows,
{
"issued_to": "myservice_account_emailid",
"audience": "myservice_account_emailid",
"scope": "https://www.googleapis.com/auth/tracks",
"expires_in": 1300,
"access_type": "offline"
}
which means still my token is valid, but if i make request to google tracks api from my application, using the same access_token, am getting response as below ,
Response: {
"error": {
"errors": [
{
"domain": "global",
"reason": "authError",
"message": "Invalid Credentials",
"locationType": "header",
"location": "Authorization"
}
],
"code": 401,
"message": "Invalid Credentials"
}
}
Even i created new project in google developer console, and created new service account , and used the new credentials in application, but still getting same response. what could be the reason?

Answer 1

Found my self.
My error prone code is as below ,
var jwt = new googleapis.auth.JWT(client_email, keyFile, null, scopes, null);
jwt.authorize(function(jwtErr, tokens){
if(jwtErr){
return;
}
else{
headers = {
'content-type' : 'application/json;charset=utf-8',
'content-length': Buffer.byteLength(data),
'Authorization' : tokens.access_token
};
options = {
host: 'www.googleapis.com',
path: '/tracks/v1/entities/create',
headers : headers,
method : 'POST',
};
var post_req = https.request(options, function(res){
res.setEncoding('utf8');
res.on('data', function (chunk) {
console.log('Response: ' + chunk);
});
});
post_req.on('error', function(error_msg){
console.log(error_msg);
});
post_req.write(data);
post_req.end();
}
});
The problem is in header object, 'Authorization' field is set to only access.token value, along with that we must specify token_type value also.
so header must be like below.
headers = {
'content-type' : 'application/json;charset=utf-8',
'content-length': Buffer.byteLength(data),
'Authorization' : tokens.token_type+' '+tokens.access_token
};
and now it solves 401 Invalid Credentials error.