How to Save Token in Local Storage Using Shared Preferences in Flutter

Discover how to effectively save and retrieve tokens in local storage with shared preferences in Flutter. This guide includes code snippets and explanations to help you implement token storage in your application.
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This video is based on the question https://stackoverflow.com/q/74064101/ asked by the user 'sharon' ( https://stackoverflow.com/u/19132574/ ) and on the answer https://stackoverflow.com/a/74064195/ provided by the user 'pmatatias' ( https://stackoverflow.com/u/12838877/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Save Token in Local Storage Using Shared Preferences in Flutter

When building applications with user authentication, managing authentication tokens is crucial for secure communication with your server. In Flutter, SharedPreferences is a great way to save user data such as tokens locally. This post will walk you through a common problem many developers face: saving a token in local storage with shared preferences, especially after a successful login.

The Problem

Imagine that you have a Flutter application where users log in using their credentials. After a successful login, you receive an authentication token from your server that needs to be saved locally to maintain user sessions. However, if not saved correctly, you might encounter errors such as a 401 Unauthorized response when trying to access user data.

In this guide, we will look at how to store this token safely within the local storage and retrieve it whenever needed.

The Solution

Let’s go step-by-step on how to properly save the token using SharedPreferences. We will incorporate the solution into your existing login function. Here’s how you can approach it:

Step 1: Check Token After Login

You already have a login function that successfully handles user authentication and returns a user object. You need to modify this function to save the token after a successful response.

Updated Login Function

In your existing function, after confirming a successful login (status code 200), add a line to save the token.

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Step 2: Utilizing SharedPreferences

Ensure you have the shared_preferences package included in your pubspec.yaml:

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Step 3: Implementing Storage Logic

Here’s how you can implement the UtilSharedPreferences class. This class contains methods for saving and retrieving the token:

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Step 4: Handling Token Retrieval

When you need to make API requests that require the token, you can easily retrieve it:

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By integrating these steps, you ensure that upon a successful login, the token is saved in the local storage and can be accessed whenever your application needs to authenticate the user.

Conclusion

Managing user authentication tokens is simplified by using SharedPreferences in Flutter. By following the steps outlined in this post, you can effectively save your token after user login and retrieve it for subsequent API requests, avoiding common issues such as unauthorized access.

If you follow these practices, your app will have a more robust authentication mechanism, improving the overall user experience. Don't hesitate to reach out if you have any questions or run into issues implementing this solution!