# Authentication

The YieldFi SDK uses EVM wallet signatures for user authentication. This provides a secure, non-custodial authentication mechanism that doesn't require passwords or API keys.

### Authentication Flow

The authentication process follows these steps:

1. **Generate Nonce** - Request a unique message to sign
2. **Sign Message** - User signs the message with their wallet
3. **Login** - Submit signature to receive access and refresh tokens
4. **Store Tokens** - Store tokens in your application (localStorage, sessionStorage, etc.)
5. **Use Tokens** - Include access token in authenticated API requests
6. **Refresh** - Refresh access token when it expires

### Key Concepts

#### Wallet-Based Authentication

Users authenticate using their Ethereum wallet (MetaMask, WalletConnect, etc.). No passwords or usernames are required.

#### Token Management

**Important:** The SDK does **not** store tokens internally. You are responsible for:

* Storing tokens securely
* Retrieving tokens when needed
* Refreshing expired tokens
* Clearing tokens on logout

#### Access Tokens

Access tokens are JWT tokens that authenticate API requests. They have a limited lifetime (typically 15 minutes) and must be refreshed periodically.

#### Refresh Tokens

Refresh tokens are used to obtain new access tokens without requiring the user to sign again. They have a longer lifetime (typically 7 days).

### Quick Example

```typescript
import { YieldFiSDK } from "yieldfi-sdk";
import { ethers } from "ethers";

const sdk = await YieldFiSDK.create({
  gatewayUrl: "https://gw.yield.fi",
});

// 1. Generate nonce
const nonce = await sdk.auth.generateNonce({
  address: "0x...",
});

// 2. Sign with wallet
const provider = new ethers.BrowserProvider(window.ethereum);
const signer = await provider.getSigner();
const signature = await signer.signMessage(nonce.message);

// 3. Login
const authResponse = await sdk.auth.login({
  address: "0x...",
  signature,
  message: nonce.message,
});

// 4. Store tokens
localStorage.setItem("accessToken", authResponse.accessToken);
localStorage.setItem("refreshToken", authResponse.refreshToken);
```

### Next Steps

* Wallet Authentication - Detailed guide on wallet authentication
* Token Management - How to manage and refresh tokens
* User Consent - Managing user consent records


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