Hack to avoid Agent DN + Password being overwritten by some ugly browser...

...s with stored site credentials.

Fixes #7038

List of browsers having the bug. Checked ones are tested successfully against.

* [X] Chromium/Chrome
* [x] Safari
* [x] ~~IE (11+)~~

Please review and test. Also open for better ideas.

**< update >**
IE 11 has no issues here at all. Only the other two.
**< /update >**

@quiqueck @ser72 @PVince81 or others please