Node中的Reddit API invalid_grant错误

Question

I am trying to implement OAuth on the reddit API. I request an authorization code, click the link, but then when I try to do a POST to get the token I get "invalid_grant" as my error. I read in their docs this means "The code has expired or already been used", but that's not possible because I just requested the code. Any help is appreciated!

This works fine...

const CLIENT_ID="*****************";
const CLIENT_SECRET="**********************";

const TYPE="code";
const RANDOM_STRING="random_string";
const URI= encodeURIComponent('http://localhost:8080/api/reddit/callback');
const DURATION="temporary";
const SCOPE_STRING="identity";
const GRANT_TYPE='authorization_code';


const router = express.Router();

router.get('/login', function(req, res){
    console.log(`Redirecting to: https://www.reddit.com/api/v1/authorize?client_id=${CLIENT_ID}&response_type=${TYPE}&state=${RANDOM_STRING}&redirect_uri=${URI}&duration=${DURATION}&scope=${SCOPE_STRING}`);
    res.redirect(`https://www.reddit.com/api/v1/authorize?client_id=${CLIENT_ID}&response_type=${TYPE}&state=${RANDOM_STRING}&redirect_uri=${URI}&duration=${DURATION}&scope=${SCOPE_STRING}`);
});

error is somewhere in here...

router.get('/callback', function(req, res){
        if (!req.query.code) throw new Error('NoCodeProvided');
        if (req.query.state != RANDOM_STRING) throw new error('Mismatched strings');
        const CODE = req.query.code;
        request('https://www.reddit.com/api/v1/access_token', {
            method: 'POST',
            form: {
              grant_type: GRANT_TYPE,
              code: CODE,
              redirect_uri: URI
            },
            auth: {
              username: CLIENT_ID,
              password: CLIENT_SECRET
            }
          }, function (error, res, body){
            if (error){
              console.log("Error: " + error);
              return;
            }
            console.log(res);
            console.log(res.access_token);
            console.log(CODE);
            //const json = res.json();
            //res.redirect(`/?token=${json.access_token}`);
          });
        });

Answer 1

Thanks to a reddit user, I discovered my callback URI was getting encoded twice. Changing to this fixed it...

const URI= 'http://localhost:8080/api/reddit/callback';