Add 2FA guide

docs/two-factor-auth/2fa-disable.md

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+## Disabling Two-Factor Authentication (2FA)
+
+
+### Disable TOTP
+
+1. Log in to your SimpleLogin account using your browser.
+2. Locate the "Two Factor Authentication" section in the account settings.
+3. Click on the "Disable TOTP" button to initiate the process. You will be prompted to enter your account password.
+4. Click on the "Submit" button to verify your identity.
+5. Click on the "Disable TOTP" button to confirm.
+
+## Disabling WebAuthn (FIDO)
+
+1. Locate the "Security Key (WebAuthn)" section in the account settings.
+2. Click on the "Manage WebAuth" button to initiate the process.
+3. You will be directed to the "Manage Your Security Key" page.
+4. Find and click the "Unlink" button next to the security key you wish to unlink.
+
+**Disabling Two-Factor Authentication (2FA) or WebAuthn (FIDO) reduces the security of your account. We strongly recommend reactivating 2FA to protect account against unauthorized access.**
+**Be reminded to re-activate 2FA later or consider using WebAuthn (FIDO) for enhanced security.**

docs/two-factor-auth/2fa-setup.md

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+## Enable Two-Factor Authentication (2FA)
+
+To begin the setup process:
+
+1. Log in to your SimpleLogin account using your browser.
+2. Head to the "Settings" section located in the top-right corner of your dashboard.
+3. Navigate to the "Security" or "Security Settings" tab to configure your authentication options.
+
+## Authenticator App Setup
+
+1. Locate the "Two Factor Authentication" option.
+2. Press "Setup TOTP" button to enable 2FA. You will have to enter your account password for security verification.
+3. Select a 2FA application on your phone or PC (e.g., Proton Pass, Aegis)
+4. Scan the provided QR code or manually enter the secret key into the app.
+5. Retrieve the 6-digit token generated by the authenticator
+
+## Security Key Authentication Setup
+
+1. Locate the "Security Key (WebAuthn)" option.
+2. Click on "Setup WebAuth" to initiate the Security Key setup process.
+3. Provide a name for your key (required) for easy identification.
+4. Click on "Register Key" to complete the registration process. You shoud follow your browser instructions to register your security key with SimpleLogin.
+
+## Recovery codes
+
+After setting up 2FA, you will see recovery codes. Store recovery codes in a safe and easily accessible location, considering using a secure physical drive (recommended) or password manager. Be aware that each recovery code is single-use and can't be used several times. 
+We recommend to keep track of used and unused codes to maintain account accessibility.

mkdocs.yml

@@ -49,6 +49,9 @@ nav:
     - Anti-phishing: getting-started/anti-phishing.md
     - Other email alias service: getting-started/compatibility-email-alias.md
     - Troubleshooting: getting-started/troubleshooting.md
+  - Two factor authentication:
+    - Enabling 2FA: /two-factor-auth/2fa-setup.md
+    - Disabling 2FA: /two-factor-auth/2fa-disable.md
   - Custom Domain:
     - Add a Custom Domain: custom-domain/add-domain.md
     - Manage your domain: custom-domain/manage-domain.md