Call web request with REST API and OAuth 2.0

Hello All

We use SP2016 onprem with Nintex 2016 Workflow v.4.6
I am looking for a way to use the Web Request to authenticate to a service via REST APPI and OAuth.

Is this possible?

The provider we use [Dracon] have stated this:

In order to obtain a token, you need to send a POST request to our token endpoint https://[host]/oauth/token
 

POST
Header:
Authorization: Basic $client_auth

Body:
grant_type = password
username = $user_name
password = $password

You need an OAuth client to authenticate – for simplicity, we used the client "DRACOON Legacy scripting support". Once the flow works correctly, it can be updated to a custom own app.
The variable $client_auth​ consists of a Base64-encoded string of $clientID:$clientSecret​
For the above mentioned OAuth client, the Client ID is dracoon_legacy_scripting and there is no client secret, therefore the string to convert to Base64 is dracoon_legacy_scripting:​ and equals ZHJhY29vbl9sZWdhY3lfc2NyaXB0aW5nOg​.

I have tried to perform the steps by using the WEB REQUEST:

When executed the following error appears:

Response status code: 401 Response content: {"error":"invalid_client","error_description":"Client authentication needed."}

Viewing the process via F12 > Network > JSON Response

"Response status code: 401 Response content: {""error"":""invalid_client"