Using scripts for automated login on Sophos systems

I spent several weeks automating captive portal logins at an education site. The wired network forced a browser login to a Sophos captive portal. Phones and lab PCs failed to stay connected without repeated manual sign‑in. I wrote small scripts that post credentials to the portal, then hooked them into startup and network events. This guide shows how I did it, what I watched for, and how you can copy the approach for internet access in an education setting.

Getting Started with Sophos Authentication Automation

Understanding the need for automation

A campus or classroom often has devices that cannot complete a browser-based login. Tablets, printers and some lab gear do not handle redirection well. That blocks internet access and slows lessons. Sophos can present a captive portal or require a separate authentication client. Those two methods may use different protocols or certificates. Before automating, check which method actually grants access for the device type you have.

What I do first:

• Confirm whether the portal is a simple HTTP form, a JSON API, or an 802.1X flow. A browser login that accepts username and password is likely a form POST. An authentication client often uses certificate provisioning or RADIUS.
• Log in manually from a browser and capture the request. I use the browser dev tools Network tab or tcpdump on a gateway.
• Note URLs, form field names, cookies, and any CSRF token. That gives the ingredients for a script.

Setting up the environment

Decide where the script will run. Options I use:

• A central gateway or travel router that stays authenticated and shares a single MAC address for devices.
• A single desktop that acts as a jump box and runs a scheduled login script.
• Individual device scripts for lab PCs or Raspberry Pis.

On Linux, install curl, jq and cron or systemd. On Windows, use PowerShell and Task Scheduler. On macOS, use launchd or a cron wrapper. Make sure the device clock is accurate. Time skew can break certificate‑based flows.

Network configuration to check:

• DHCP lease behaviour. If the portal ties access to an IP or MAC, renewals may force re-authentication.
• DNS and captive portal redirects. Some devices cache DNS; add a short TTL if you control local DNS.

Script requirements and considerations

Keep the script small and transparent. My checklist:

• Handle HTTPS. If the portal uses HTTPS with an unknown CA, either import the CA into the device or use curl with a pinned certificate file. Do not disable certificate checks on production endpoints.
• Preserve cookies and session headers. Use a cookie jar file or PowerShell session object.
• Retry with backoff. A single failed POST should not lock the account.
• Log success or failure to a file with timestamps.
• Store credentials securely. On Linux, use a protected file with 600 permissions or a simple keyring. On Windows, use the credential manager and fetch credentials at runtime.

I avoid hardcoding passwords inside scripts. For small labs I store credentials in a file readable only by the service account and rotate them when the institution changes passwords.

Implementing Scripts for Automated Login

Writing the script

Start by reproducing the browser POST. Example Linux curl flow for a typical form POST:

bash

!/bin/bash

COOKIEJAR=”/var/run/sophoscookie.txt”
LOGINURL=”https://10.0.0.1/login”
USERNAME=”schooluser”
PASSFILE=”/etc/sophos/pass”
PASSWORD=”$(cat $PASSFILE)”

Get any CSRF token from the login page

TOKEN=$(curl -sk -c $COOKIEJAR “$LOGIN_URL” | sed -n ‘s/.name=”csrf” value=”([^”])”.*/\1/p’)

Post credentials

curl -sk -b $COOKIEJAR -c $COOKIEJAR \
-d “username=$USERNAME” \
-d “password=$PASSWORD” \
-d “csrf=$TOKEN” \
“$LOGINURL” -o /tmp/sophoslogin_response.html

Check for a success marker in the response

grep -q “Welcome” /tmp/sophosloginresponse.html && echo “$(date): login ok” >> /var/log/sophos_login.log

On Windows use PowerShell Invoke-WebRequest with -SessionVariable for cookies. Keep the script short so you can debug one step at a time.

If the portal uses JSON or an API, adapt the curl command to send a JSON body and set Content-Type: application/json. If the authentication client is required, scripts will not help; you must either deploy the client or use a device that can run it.

Testing the script

Test manually before automating. Steps I follow:

1. Run the script while watching the browser dev tools or tcpdump. Confirm the same requests are sent.
2. Check cookie files and response HTML for expected values.
3. Simulate failure modes by providing a wrong password and check the script logs a clear error.
4. Test on a clean device that has never authenticated. That reveals hidden dependencies such as required headers or referer checks.

Once manual tests pass, run the script at boot or when the network interface comes up. On systemd systems use a service unit that depends on network-online.target. On Windows use Task Scheduler with trigger set to log on and on network connect.

Troubleshooting common issues

Login fails but browser login works:

• The portal may set a session tied to a user agent or browser fingerprint. Set the script to use the same User-Agent and headers as the browser.
• Check for JS-generated tokens. If the login page runs JavaScript to build a token, you will need to replicate that logic or use a headless browser like Puppeteer for automation.

Certificates and HTTPS failures:

• If curl complains about a self-signed CA, import the CA or point curl to a CA bundle. Do not skip verification on devices that handle sensitive data.
• Check the device clock. Large clock drift can cause TLS failures.

Frequent re-authentication:

• The portal may tie access to MAC or require client certificates. If it is MAC-based, use a travel router and MAC cloning to present one authenticated device to the portal while other devices sit behind NAT.
• For client-certificate flows, deploy the client or the certificate to devices that need persistent access.

Performance and lockouts:

• Limit retries and add a cooldown. Too many failed attempts may lock the account. Log each attempt so you can spot loops.

Final notes and takeaways
Automating captive portal login on Sophos is often straightforward when the portal is a simple form. The main tasks are capturing the browser request, handling cookies and tokens, and running the script at the right network event. If Sophos requires a client or client certificates, scripts will not replace that. For mixed-device labs I prefer a single authenticated gateway device or a travel router that keeps a single session alive and shares internet access. Keep credentials safe, log clearly, and run small tests before rolling anything into production.