How to Get a Token API with Fetch: A Step-By-Step Guide

Learn how to successfully retrieve a `Token API` using the Fetch API in JavaScript. A clear guide to resolving authentication issues! --- This video is based on the question https://stackoverflow.com/q/64223029/ asked by the user 'scorval' ( https://stackoverflow.com/u/12118119/ ) and on the answer https://stackoverflow.com/a/64223509/ provided by the user 'kavigun' ( https://stackoverflow.com/u/3202440/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to get a Token API with fetch Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- How to Get a Token API with Fetch: A Step-By-Step Guide If you've ever tried to access an API that requires authentication, you know how challenging it can be to get the token you need to make requests. One common situation involves using the Fetch API in JavaScript to retrieve a token for services like "ile de France mobilité". In this guide, we will tackle the problem step-by-step, focusing on how to correctly configure your Fetch call to avoid common pitfalls such as 401 Unauthorized errors. Understanding the Problem In your case, you are attempting to authenticate using OAuth 2.0 and have set up your Fetch request. However, you're receiving a 401 Unauthorized status code. This means that the server is rejecting your request due to invalid authentication credentials. This suggests there might be an issue with the format of the body you're sending, which is crucial for authentication. Let's break down the solution to resolve this issue. Solution Overview Step 1: Correctly Formatting the Body The Fetch API accepts the body of the request as a string when sending URL encoded data. You should structure your body as a single string where key-value pairs are concatenated with &. Here’s how you should format it: [[See Video to Reveal this Text or Code Snippet]] Step 2: Complete Fetch Request Example Here’s your corrected Fetch request using the new body format: [[See Video to Reveal this Text or Code Snippet]] Step 3: Calling the Fetch Function You also mentioned needing to call this function from an HTML file. Here’s how you can set it up: [[See Video to Reveal this Text or Code Snippet]] Step 4: Verify Your Server Setup Make sure your server is properly set up to handle requests. In your server code, ensure you’re using the necessary middlewares, like bodyParser, to parse JSON requests effectively: [[See Video to Reveal this Text or Code Snippet]] Conclusion With this guide, you should now be able to retrieve a token from the ile de France mobilité API using Fetch in JavaScript. Just remember, formatting the body correctly and ensuring your server is set up to handle requests are crucial steps in this process. If you encounter further issues, double-check your client_id, client_secret, and the requested scopes to ensure they are correct. Happy coding!