Request to Kerberos authenticated API considered unauthorized despite having kerberos ticket in authorization header

Question

I am trying to call a Flask API endpoint (http://monarch.example.com:8080/) hosted in Apache web server in a Linux machine. This endpoint is protected by Kerberos authentication. I use kinit user to initialize Kerberos.

Then I am using python kerberos library to get the ticket and requests library for the api call. I am providing the ticket in the Authorization header of the request. Relevant code snippet for that:

`__, krb_context = kerberos.authGSSClientInit("[email protected]")
kerberos.authGSSClientStep(krb_context, "")
auth_header = ("Negotiate " + kerberos.authGSSClientResponse(krb_context))
headers = {"Authorization": auth_header}`

I have checked that the Authorization header is populated with a value.

However I get 401-unauthorized as response.

The Kerberos configuration from /etc/apache2/sites-available/monarch.conf for the Service containing the endpoint is:

<Directory /var/www/monarch>
       AuthType Kerberos
       AuthName "Acme Corporation"
       KrbAuthRealms EXAMPLE.COM
       KrbMethodNegotiate Off
       KrbSaveCredentials Off
       KrbVerifyKDC Off
       KrbMethodK5Passwd On
       # Krb5Keytab /etc/apache2/http.keytab
       Krb5keytab /etc/krb5.keytab
       Require user [email protected]
</Directory>

Lastly, the list of principals is:

host/[email protected]
HTTP/[email protected]
K/[email protected]
kadmin/[email protected]
kadmin/[email protected]
krbtgt/[email protected]
[email protected]
root/[email protected]

I have been stuck with this problem for a few days now. It would be great if anyone can help me in this regard.