On the "Trusted certificate authorities for SSL" edit page, each manually added CA now has a panel to the right of its PEM text box showing Issuer, Subject, Validity and Fingerprint.

How it works:

• It's one GUI plugin file, set up like your auto_reload_toggle MKP. It wraps the method that draws each CA's input field (_CAorCAChain.render_input in cmk/gui/valuespec/definitions.py):
  it draws the original input in a left column and the details in a right column.
• Validity is shown as two lines, "Not before" and "Not after". A certificate that is not yet valid or has expired gets a red "(not valid)" marker.
• The fingerprint is SHA256, colon-separated.
• If a PEM holds a chain, there is one block per certificate, labelled "Certificate 1 of N".
• If the content is empty or can't be parsed, the page looks exactly as before.

Limitations:

• No live update: the details are worked out when the page loads, so a certificate you've just pasted shows its details only after you save or submit the form. Live updates would need an
  extra small ajax endpoint and some JavaScript; I can add that if you want it.