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3 minute read - API Testing API Challenges

Challenge 29 - How To - Authentication 401

Jul 24, 2021

This post and video shows how to complete the authentication failed with username and password challenge number 29, which returns a status code of 401.

What are the API Challenges?

Our API Challenges Application has a fully functional cloud hosted API, and a set of challenges to work through.

Authentication Challenge

Most of the challenges simply require the correct payload, and an X-Challenger header to track the session. The authentication challenges require an extra header, the value for which can only be obtained with a username and password.

Challenge 29 Authentication Failed

Issue a POST request on the /secret/token end point and receive 401 when Basic auth username/password is not admin/password

  • POST request means use the HTTP Verb POST
    • e.g. POST /secret/token sends to the secret token endpoint
  • Basic auth means include the Basic Authorization header
  • username/password is not admin/password the authorisation header value is base 64 encoded, and the details should not match admin as the username, and password for the password
  • add the X-CHALLENGER header to track progress and because the authentication code we need is asociated with the X-challenger session
  • Receive a 401 response

Basic Instructions

  • Create a new request for the /secret/token end point
    • if running locally that endpoint would be
      • http://localhost:4567/secret/token
    • if running in the cloud that endpoint would be
  • The verb should be a POST
  • Add a Basic Auth header by selecting “Basic” from the “Auth” tab and entering a username and password but make sure it is not admin/password e.g. use username “Admin1”, password “Pa55word” (or anything else you want)
  • There should be no payload in the message
  • You should receive a 401 response - meaning “Unauthorized” because you entered the wrong username or password
  • The request should have an X-CHALLENGER header to track challenge completion
> POST /secret/token HTTP/1.1
> Host:
> User-Agent: insomnia/2021.2.2
> X-CHALLENGER: x-challenger-guid
> Authorization: Basic YWRtaW46cGFzc3dvcmRk
> Accept: */*
> Content-Length: 0

< HTTP/1.1 401 Unauthorized
< Connection: close
< Date: Sat, 24 Jul 2021 11:13:04 GMT
< Www-Authenticate: Basic realm="User Visible Realm"
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Headers: *
< X-Challenger: x-challenger-guid
< Content-Type: text/html;charset=utf-8
< Server: Jetty(9.4.z-SNAPSHOT)
< Via: 1.1 vegur

Note that the Authorization header does not send the username and password in plain text, it uses Base64 to obscure the details.

You could see what username and password I used by typing the Base64 string YWRtaW46cGFzc3dvcmRk into a Base64 decoder like

Or you could decode it in the browser dev console by typing:


The command to encode a string as base64 is btoa

Note also that although we add an “Authorization” header, really we are trying to “authenticate” with a set of user details.

  • Authorization is “do you have the right permissions”
  • Authentication is “are you who you say you are”


  • try creating a base64 Authorization header by hand, without using the “Auth” tab in Insomnia

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