Technical Tip: Collect mobile numbers in FortiAP Captive Portal

FortiGate does not natively validate mobile numbers, but customization can be done in the captive portal HTML page to include a mobile number input field. The submitted data can then be logged or forwarded to an external system for tracking.

1. Enable captive portal.

Go to Network -> Interfaces. Select the interface or SSID where captive portal should apply. Under Authentication, enable Captive Portal. Choose the type of captive portal (Authentication / Disclaimer + Authentication).

2. Edit the captive portal page: 

Navigate to System -> Replacement Messages. Select Authentication -> Login Page. Switch to HTML view. Insert a new input field for mobile number.

Example:

<div class="field">
    <label for="ft_mobile">Mobile Number</label>
        <div>
            <input name="MOBILENUMBER" id="ft_mobile" type="text" placeholder="<Enter mobile number>">
        </div>
</div>

3. Logging and Storage:

• FortiGate will authenticate users based only on username and password.

• The MOBILENUMBER field will be passed in the HTTP POST data.

• Options to store this information:

  • Enable syslog logging and parse POST requests.

  • Use an external RADIUS/LDAP server that can capture additional POST variables.

  • Export logs for compliance or guest reporting.

Below are the limitations:

• No OTP validation - mobile number is only collected, not verified.

• If SMS validation is required, integration with FortiAuthenticator or a third-party portal/SMS gateway is needed.

• Data capture depends on logging/monitoring setup.