Tell me about the keygen tag.

The <keygen> tag was used for generating a key pair (public and private) and sending the public key to the server. It was intended for managing client certificates.

It had the following attributes (most common):

• name: The name of the form element for submitting the public key.
• disabled: Disables the element.
• form: The ID of the form to which the element belongs.
• keytype: The type of key generated (e.g., rsa).
• challenge: A string linking the generated key to a specific request.

Example of usage (although now deprecated):

<form action="/process" method="post">
  <keygen name="cert" keytype="rsa">
  <input type="submit">
</form>

The generated public key was sent to the server in PKCS#10 encoding.

Important: The <keygen> tag is deprecated and has been removed from the HTML5 specification. Its functionality was complex to use and had limited application. Modern approaches to managing client certificates and web application security use other mechanisms, such as the Web Crypto API.