error: "unsupported_grant_type" using reddit API, javascript

Question

During the Oauth process for reddit API, I have gotten stuck at the access token request, getting an error saying 'unsupported_grant_type'. The API documentation says to use grant type 'authorization_code' which is what I have set now. I've tried using a string, URLSearchParams, and formData to correct it thinking that it was the format that was breaking it but nothing has worked.

Here is the function in question:

async function fetchAccessToken(){
    console.log("fetching access token...");

    

    const cred = btoa(`${client_id}:${client_secret}`);

    var form = new FormData()
    form.append('code', authCode)
    form.append('grant_type', grantType)
    form.append('redirect_uri', redirect_uri)

    const response = await fetch('https://ssl.reddit.com/api/v1/access_token', {
        method: 'POST',
        headers: {
            'Content-Type':"application/x-www-form-urlencoded",
            'Authorization':`Basic ${cred}`
            },
        body: form
        })

    const data = await response.json();

    console.log(response.status);//says 200
    console.log(data);//says {error: 'unsupported_grant_type'}
    }

I've been stuck here for over a week, any help would be appreciated.

Answer 1

I was stuck on a similar issue - ended up using Axios. Make sure to add a unique 'User-Agent'.

const axios = require("axios").default;
const url = require("url");

async function fetchAccessToken(){
console.log("fetching access token...");

const client_id = "";
const client_secret = "";
const username = "":
const password = "";

const authData = {
    grant_type: "password",
    username: username,
    password: password,
};

const params = new url.URLSearchParams(authData);

const response = await axios({
url: 'https://www.reddit.com/api/v1/access_token',        
method: 'POST',
    headers: {
        'User-Agent': "myApp:V0.1 by Dschaar", //some unique user agent
        },
    auth: {
       username: username,
       password: password,
    }
    params: params
})

console.log(response.data);
}