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Authentication

Authentication in Flow Client Library (FCL) is closely tied to the concept of currentUser. In fact, fcl.authenticate and fcl.unauthenticate are simply aliases for fcl.currentUser.authenticate() and fcl.currentUser.unauthenticate(), respectively. So, let’s take a closer look at currentUser.

As an onchain app developer who uses FCL, the primary authentication functionalities revolve around how to:

  • Determine the currentUser and whether they are logged in.
  • Log a user in.
  • Log a user out.

Due to the way FCL works, to log in and sign up are essentially the same process.

Retrieve information about the current user

FCL provides two ways to get information about the current user:

  1. A promise-based method that returns a snapshot of the user’s data.
  2. A subscription-based method that triggers a callback function with the latest user information whenever it changes.

Snapshot of the current user​


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import * as fcl from '@onflow/fcl';
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const currentUser = await fcl.currentUser.snapshot();
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console.log('The Current User:', currentUser);

Subscribe to the Current User​


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import * as fcl from '@onflow/fcl';
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// Returns an unsubscribe function
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const unsubscribe = fcl.currentUser.subscribe((currentUser) => {
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console.log('The Current User:', currentUser);
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});

Authenticate and unauthenticate

The TL;DR: Call fcl.authenticate() to log in and fcl.unauthenticate() to log out.

On Flow mainnet, no additional configuration is needed, because your app’s users will go through the authentication process and can use any FCL-compatible wallet provider.

During development, you’ll likely want to configure your app to use @onflow/dev-wallet. The Quick Start guide will walk you through how to set it up.

We also recommend that you use the FCL Discovery Service to help users discover and connect to FCL-compatible wallets.

Whether you're new to building onchain, or an established veteran, we’re here to help. If you run into any issues, reach out to us on Discord — we’re happy to assist!

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