Im using below code to get access token from Google Drive and getting error says 'Invalid grant'. Here im passing code as Auth. Provider ID. Can anyone please assist on this?
try{
//Getting access token from google
HttpRequest req = new HttpRequest();
req.setMethod('POST');
req.setEndpoint('https://accounts.google.com/o/oauth2/token');
req.setHeader('content-type', 'application/x-www-form-urlencoded');

String messageBody = 'code=' + code + '&client_id=' + key + '&client_secret=' + secret + '&redirect_uri=' + redirect_uri + '&grant_type=authorization_code';
req.setHeader('Content-length', String.valueOf(messageBody.length()));
req.setBody(messageBody);
req.setTimeout(60 * 1000);
Http h = new Http();
String resp;
HttpResponse res = h.send(req);
resp = res.getBody();

System.debug('Response :::' + resp);
JSONParser parser = JSON.createParser(resp);
while (parser.nextToken() != null) {
if ((parser.getCurrentToken() == JSONToken.FIELD_NAME)) {
String fieldName = parser.getText();
parser.nextToken();
if (fieldName == 'access_token') {
accesstoken = parser.getText();
} else if (fieldName == 'expires_in') {
expiresIn = parser.getIntegerValue();
} else if (fieldname == 'token_type') {
tokentype = parser.getText();
}

} }
} catch
(Exception e) {
System.debug(LoggingLevel.ERROR,'Call exception ' + e.getMessage());
}
System.debug('access token ::::' + accesstoken);