Server gives application/json response when Kerberos Auth fails

[fjf2002]

Describe the bug

(At least some) Kerberos Login Errors result in a webserver response of Content-Type application/json .

To Reproduce

Steps to reproduce the behavior:

1. Remove Kerberos Auth Keytab File
2. In Your browser, load the login page
3. The Browser will reveive a response with Content-Type application/json and content

{
"success": 0,
"errormsg": "Object of type MissingCredentialsError is not JSON serializable",
"info": "",
"result": null,
"data": null
}

Expected behavior
Some meaningful error message of Content-Type text/html should be sent.

Desktop (please complete the following information):

• OS: Windows 11
• pgAdmin version: 9.17 Docker Image
• Mode: Server
• Browser Chrome
• Package type: Container