Mobile App Email Verification

TL;DR

The best approach to confirm email addresses within a mobile app is to send a verification link via email after signup. This link should contain a unique token that, when clicked, confirms the user’s address and activates their account. Implement robust error handling and provide clear feedback to the user throughout the process.

Step-by-step Guide

1. Signup Process: Collect Email Address

• When a new user signs up, collect their email address.
• Validate the email format on the client-side (basic check) to improve user experience. Don’t rely solely on this; server-side validation is crucial.

Generate a Unique Verification Token

• After successful signup, generate a unique token associated with the user’s email address. This token should be long and random to prevent guessing.
• Store this token securely in your database (e.g., linked to the user record). Include an expiry timestamp for security.

# Example Python using a library like secrets
import secrets
token = secrets.token_urlsafe(32) # Generates a 32-character random token

Send the Verification Email

• Use an email service provider (ESP) like SendGrid, Mailgun, or AWS SES to send a verification email.
• The email should contain a link with the unique token embedded in it. The link format might look like this: https://yourapp.com/verify?token=YOUR_TOKEN
• Ensure the email is well-formatted and includes clear instructions for the user.

Handle the Verification Link Click

• When a user clicks the verification link, your server should extract the token from the URL.
• Validate the token against your database:
• Check if the token exists.
• Check if the token has expired.
• Ensure the token hasn’t already been used.

Confirm Email and Activate Account

• If the token is valid, mark the user’s email as verified in your database.
• Activate the user’s account (e.g., set a status flag to ‘active’).
• Redirect the user to a success page or their app dashboard.

Error Handling and User Feedback

• Invalid Token: If the token is invalid, display an error message to the user (e.g., “Invalid verification link”).
• Expired Token: If the token has expired, prompt the user to request a new verification email.
• Token Already Used: If the token has already been used, inform the user that their email is already verified.
• Email Sending Failure: Handle potential email sending failures gracefully and provide an option for the user to retry or contact support.

Resend Verification Email Feature

• Provide a “Resend Verification Email” feature in your app. This should generate a new token and send another verification email.

Security Considerations

• Token Length: Use sufficiently long tokens (at least 32 characters) to prevent brute-force attacks.
• Token Expiry: Set a reasonable expiry time for the token (e.g., 24 hours).
• Rate Limiting: Implement rate limiting on verification email requests to prevent abuse.
• HTTPS: Ensure all communication is over HTTPS to protect tokens from interception.
• Input Validation: Thoroughly validate the email address on the server-side to prevent injection attacks.