email-and-password-best-practices

name	email-and-password-best-practices
description	This skill provides guidance and enforcement rules for implementing secure email and password authentication using Better Auth.

Email Verification Setup

When enabling email/password authentication, configure emailVerification.sendVerificationEmail to verify user email addresses. This helps prevent fake sign-ups and ensures users have access to the email they registered with.

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.

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

While Better Auth validates inputs server-side, implementing client-side validation is still recommended for two key reasons:

1. Improved UX: Users receive immediate feedback when inputs don't meet requirements, rather than waiting for a server round-trip.
2. Reduced server load: Invalid requests are caught early, minimizing unnecessary network traffic to your auth server.

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.

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

Password Reset Flows

Password reset flows are essential to any email/password system, we recommend setting this up.

To allow users to reset a password first you need to provide sendResetPassword function to the email and password authenticator.

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

Better Auth implements several security measures in the password reset flow:

Timing attack prevention

• Background email sending: Better Auth uses runInBackgroundOrAwait internally to send reset emails without blocking the response. This prevents attackers from measuring response times to determine if an email exists.
• Dummy operations on invalid requests: When a user is not found, Better Auth still performs token generation and a database lookup (with a dummy value) to maintain consistent response times.
• Constant response message: The API always returns "If this email exists in our system, check your email for the reset link" regardless of whether the user exists.

On serverless platforms, configure a background task handler to ensure emails are sent reliably:

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

Token security

• Cryptographically random tokens: Reset tokens are generated using generateId(24), producing a 24-character alphanumeric string (a-z, A-Z, 0-9) with high entropy.
• Token expiration: Tokens expire after 1 hour by default. Configure with resetPasswordTokenExpiresIn (in seconds):

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

• Single-use tokens: Tokens are deleted immediately after successful password reset, preventing reuse.

Session revocation

Enable revokeSessionsOnPasswordReset to invalidate all existing sessions when a password is reset. This ensures that if an attacker has an active session, it will be terminated:

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

Redirect URL validation

The redirectTo parameter is validated against your trustedOrigins configuration to prevent open redirect attacks. Malicious redirect URLs will be rejected with a 403 error.

Password requirements

During password reset, the new password must meet length requirements:

• Minimum: 8 characters (default), configurable via minPasswordLength
• Maximum: 128 characters (default), configurable via maxPasswordLength

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

Sending the password reset

Once the password reset configurations are set-up, you can now call the requestPasswordReset function to send reset password link to user. If the user exists, it will trigger the sendResetPassword function you provided in the auth config.

const data = await auth.api.requestPasswordReset({
    body: {
        email: '[e-mail]', // required
        redirectTo: 'https://example.com/reset-password',
    },
});

Or authClient:

const { data, error } = await authClient.requestPasswordReset({
    email: '[e-mail]', // 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

Better Auth uses scrypt by default for password hashing. This is a solid choice because:

• It's designed to be slow and memory-intensive, making brute-force attacks costly
• It's natively supported by Node.js (no external dependencies)
• OWASP recommends it when Argon2id isn't available

Custom Hashing Algorithm

To use a different algorithm (e.g., Argon2id), provide custom hash and verify functions in the emailAndPassword.password configuration:

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.