portal/.agents/skills/email-and-password-best-practices/SKILL.md

---
name: email-and-password-best-practices
description: Configure email verification, implement password reset flows, set password policies, and customise hashing algorithms for Better Auth email/password authentication. Use when users need to set up login, sign-in, sign-up, credential authentication, or password security with Better Auth.
---

## Quick Start

1. Enable email/password: `emailAndPassword: { enabled: true }`
2. Configure `emailVerification.sendVerificationEmail`
3. Add `sendResetPassword` for password reset flows
4. Run `npx @better-auth/cli@latest migrate`
5. Verify: attempt sign-up and confirm verification email triggers

---

## Email Verification Setup

Configure `emailVerification.sendVerificationEmail` to verify user email addresses.

```ts
import { betterAuth } from 'better-auth';
import { sendEmail } from './email'; // your email sending function

export const auth = betterAuth({
	emailVerification: {
		sendVerificationEmail: async ({ user, url, token }, request) => {
			await sendEmail({
				to: user.email,
				subject: 'Verify your email address',
				text: `Click the link to verify your email: ${url}`
			});
		}
	}
});
```

**Note**: The `url` parameter contains the full verification link. The `token` is available if you need to build a custom verification URL.

### Requiring Email Verification

For stricter security, enable `emailAndPassword.requireEmailVerification` to block sign-in until the user verifies their email. When enabled, unverified users will receive a new verification email on each sign-in attempt.

```ts
export const auth = betterAuth({
	emailAndPassword: {
		requireEmailVerification: true
	}
});
```

**Note**: This requires `sendVerificationEmail` to be configured and only applies to email/password sign-ins.

## Client Side Validation

Implement client-side validation for immediate user feedback and reduced server load.

## Callback URLs

Always use absolute URLs (including the origin) for callback URLs in sign-up and sign-in requests. This prevents Better Auth from needing to infer the origin, which can cause issues when your backend and frontend are on different domains.

```ts
const { data, error } = await authClient.signUp.email({
	callbackURL: 'https://example.com/callback' // absolute URL with origin
});
```

## Password Reset Flows

Provide `sendResetPassword` in the email and password config to enable password resets.

```ts
import { betterAuth } from 'better-auth';
import { sendEmail } from './email'; // your email sending function

export const auth = betterAuth({
	emailAndPassword: {
		enabled: true,
		// Custom email sending function to send reset-password email
		sendResetPassword: async ({ user, url, token }, request) => {
			void sendEmail({
				to: user.email,
				subject: 'Reset your password',
				text: `Click the link to reset your password: ${url}`
			});
		},
		// Optional event hook
		onPasswordReset: async ({ user }, request) => {
			// your logic here
			console.log(`Password for user ${user.email} has been reset.`);
		}
	}
});
```

### Security Considerations

Built-in protections: background email sending (timing attack prevention), dummy operations on invalid requests, constant response messages regardless of user existence.

On serverless platforms, configure a background task handler:

```ts
export const auth = betterAuth({
	advanced: {
		backgroundTasks: {
			handler: (promise) => {
				// Use platform-specific methods like waitUntil
				waitUntil(promise);
			}
		}
	}
});
```

#### Token Security

Tokens expire after 1 hour by default. Configure with `resetPasswordTokenExpiresIn` (in seconds):

```ts
export const auth = betterAuth({
	emailAndPassword: {
		enabled: true,
		resetPasswordTokenExpiresIn: 60 * 30 // 30 minutes
	}
});
```

Tokens are single-use — deleted immediately after successful reset.

#### Session Revocation

Enable `revokeSessionsOnPasswordReset` to invalidate all existing sessions on password reset:

```ts
export const auth = betterAuth({
	emailAndPassword: {
		enabled: true,
		revokeSessionsOnPasswordReset: true
	}
});
```

#### Password Requirements

Password length limits (configurable):

```ts
export const auth = betterAuth({
	emailAndPassword: {
		enabled: true,
		minPasswordLength: 12,
		maxPasswordLength: 256
	}
});
```

### Sending the Password Reset

Call `requestPasswordReset` to send the reset link. Triggers the `sendResetPassword` function from your config.

```ts
const data = await auth.api.requestPasswordReset({
	body: {
		email: 'john.doe@example.com', // required
		redirectTo: 'https://example.com/reset-password'
	}
});
```

Or authClient:

```ts
const { data, error } = await authClient.requestPasswordReset({
	email: 'john.doe@example.com', // required
	redirectTo: 'https://example.com/reset-password'
});
```

**Note**: While the `email` is required, we also recommend configuring the `redirectTo` for a smoother user experience.

## Password Hashing

Default: `scrypt` (Node.js native, no external dependencies).

### Custom Hashing Algorithm

To use Argon2id or another algorithm, provide custom `hash` and `verify` functions:

```ts
import { betterAuth } from 'better-auth';
import { hash, verify, type Options } from '@node-rs/argon2';

const argon2Options: Options = {
	memoryCost: 65536, // 64 MiB
	timeCost: 3, // 3 iterations
	parallelism: 4, // 4 parallel lanes
	outputLen: 32, // 32 byte output
	algorithm: 2 // Argon2id variant
};

export const auth = betterAuth({
	emailAndPassword: {
		enabled: true,
		password: {
			hash: (password) => hash(password, argon2Options),
			verify: ({ password, hash: storedHash }) => verify(storedHash, password, argon2Options)
		}
	}
});
```

**Note**: If you switch hashing algorithms on an existing system, users with passwords hashed using the old algorithm won't be able to sign in. Plan a migration strategy if needed.