As an admin, when you try to add (or update) an external tool (LTI), the "Shared secret" is truncated at the < character.

Steps to reproduce:

1. Login as Site Admin
2. Go to: "Site administration / Plugins / Activity modules / External tool / Manage tools"
3. Then click on "configure a tool manually"
4. Put something in "Tool name" and "Tool URL"
5. In "Shared secret" field, type text with a < character, like "rtyu<99" and validate with Enter
6. Click on the eye icon to verify the value is ok
7. Click "Save changes"
8. Re-Edit the tool, and check "Shared secret" value by clicking again on the eye (It should be "rtyu<99" but is "rtyu" )

The problem is the same if you edit a pre-existing tool.

Seen in my 3.11.7 production Moodle, on my 4.0.1+ testing Moodle and https://sandbox.moodledemo.net/ and on 4.1dev Moodle on https://qa.moodledemo.net

Certainly also existing in previous Moodle versions.

I don't know if the same problem exists in other fields of the same type, elsewhere in Moodle... would certainly be interesting to check by someone knowing well when same type of field (or code) is used.