Lab 5: HTTPS and WebAuthn

This lab will introduce you to HTTPS and WebAuthn. In part 1, you will learn about the ACME protocol for obtaining TLS certificates, and in part 2, you will add WebAuthn support to Zoobar.

Network setup

For this lab, you will need access to a few more network ports: port 5000 for the certificate authority in part 1, and port 8443 for the HTTPS version of the Zoobar web site in part 2. Add these ports to your SSH port forwarding setup as needed.

Setting up the web server

Before you begin working on these exercises, please use Git to commit your Lab 4 solutions, fetch the latest version of the course repository, and then create a local branch called lab5 based on our lab5 branch, origin/lab5. Do not merge your previous solutions into lab 5. Here are the shell commands:

student@6566-v24:~$ cd lab
student@6566-v24:~/lab$ git commit -am 'my solution to lab4'
[lab4 c54dd4d] my solution to lab4
 1 files changed, 1 insertions(+), 0 deletions(-)
student@6566-v24:~/lab$ git pull
Already up-to-date.
student@6566-v24:~/lab$ git checkout -b lab5 origin/lab5
Branch lab5 set up to track remote branch lab5 from origin.
Switched to a new branch 'lab5'
student@6566-v24:~/lab$ make

Like lab 4, the source code for lab 5 is based on the initial web server from lab 1. It does not include privilege separation or Python profiles.

You will need to start several components: the zookws web server, the HTTPS proxy (whose job will be to translate HTTPS requests for zookws), and the certificate authority (whose job will be to issue a TLS certificate for your HTTPS proxy). The commands are:

student@6566-v24:~/lab$ ./zookd 8080 &
[1] 808
student@6566-v24:~/lab$ ./ &
[2] 809
[811] 2023/03/30 13:47:17.388163 starting ghostunnel in server mode
[811] 2023/03/30 13:47:17.449362 using cert/key files on disk as certificate source
[811] 2023/03/30 13:47:17.449517 error: unable to load certificates: open tls.cert: no such file or directory
error: open tls.cert: no such file or directory
student@6566-v24:~/lab$ ./ca/ &
[3] 818
 * Serving Flask app 'run' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 111-516-085

The errors you see above from are because there is no TLS certificate yet; you will fix that in part 1.

Part 1: HTTPS certificates

To get HTTPS working, you need to obtain a TLS certificate for your web server. There is a standard protocol for obtaining a TLS certificate, called the Automatic Certificate Management Environment (ACME). The certificate authority (ca/ in our lab) uses this ACME protocol to validate requests from clients and issue certificates.

In this lab, you will need to use your browser to connect to Zoobar via HTTPS, using a certificate issued by the ACME CA server in your VM. By default, your browser does not trust this CA. You can explicitly add the CA's certificate to your browser, by downloading the root CA certificate from, and installing it in your browser. For example, in Chrome, you can add a new CA under the Authorities tab in chrome://settings/certificates (you need to manually copy-paste that URL into your address bar, because Chrome blocks links to chrome:// URLs by default).

Exercise 1: ACME client.

Implement a client,, that will obtain a TLS certifiate from the lab's ACME CA, storing the resulting key in tls.key and certificate in tls.cert.

Use as the hostname of the ACME CA server. (This points to localhost.)

For consistency, please generate a 2048-bit RSA key in tls.key, and obtain a certificate for hostname (This also points to localhost.)

There is lots of documentation you can find online on ACME and certificates. Some suggestions that might be helpful:

Use make check-lab5 to check if your ACME client correctly obtains a TLS certificate.

If you need additional Python packages to be installed for your solution to work, place the package names in requirements.txt, so that the grader will install the packages when testing your solution.

Submit your answers to the first part of this lab assignment by running make and upload the resulting file to the submission web site.

Part 2: WebAuthn

In this part, you will modify Zoobar to support login via WebAuthn. Rather than implementing two-factor authentication, you will make WebAuthn the only authentication factor: a user will register for an account using WebAuthn (no password), and will similarly log in by entering their username and using WebAuthn to authenticate (again, no password).

WebAuthn uses an authenticator to store credentials and sign attestations in response to authentication requests. You can use a physical WebAuthn authenticator for this lab, such as the FIDO2-capable Yubikey 5. You can ask IS&T for a Yubikey token.

Alternatively, you can use the virtual authenticator in Chrome to emulate an authenticator, which might make your development easier instead of using a physical authenticator device.

Warmup: WebAuthn Demo.

Practice using WebAuthn at

You will need a WebAuthn authenticator. We recommend the virtual authenticator in Chrome.

  1. Can you register via webauthn?
  2. Can you authenticate via webauthn?
  3. Can you re-register as a different user via webauthn?
  4. Do different registrations use the same credential?
  5. Can you authenticate without an authenticator (or if you delete one of the credentials in your virtual authenticator)?

Answers (Highlight to reveal): Yes, Yes, Yes, No, No

Exercise 2: Implement WebAuthn for Zoobar.

Modify the Zoobar application so that it authenticates users with WebAuthn instead of passwords.

You can remove the password entry box on the login page, but keep the login and register buttons as-is, except make them work with WebAuthn.

There are many online resources describing WebAuthn; you are welcome to use any of them. Some suggested ones are:

Use make check-lab5 to check if your WebAuthn support works correctly.

If you need additional Python packages to be installed for your solution to work, place the package names in requirements.txt, so that the grader will install the packages when testing your solution.

Don't forget to remove your VM's ACME CA root certificate from your web browser, if you installed it at the beginning of this lab!

Run make and upload to the submission web site, and you're done!