**Related issue:** Resolves#36774
# Checklist for submitter
If some of the following don't apply, delete the relevant line.
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.
## Testing
- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Certificate templates now support additional variables for subject
names and SANs, including host platform and identity-provider-derived
fields such as username (local part), groups, department, and full name.
* **Bug Fixes**
* Improved validation and error handling for missing host or
identity-provider data during template variable substitution.
* **Tests**
* Expanded coverage for supported/unsupported variables, correct
placeholder replacement, caching behavior, and RFC 4514 escaping in
DN-related values.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
Konstantin Sykulev
a93c61722d