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Solved: How do I debug Kerberos authentication in FortiProxy?

This article describes a working WAD debug flow for Kerberos authentication as an authentication method.

Solution

In this scenario, the FortiProxy has enforced to challenge the client browser with Kerberos as an authentication method.

Kerberos Authentication Flow:

Kerberos Authentication Flow

The following command can be used to capture and save the WAD debug outputs:

# diag wad filter src <IP address>
# diag wad debug enable category auth
# diag wad debug enable category policy
# diag wad debug enable level verbose
# diag debug application fnbamd -1
# diag debug enable

Example of debugging outputs.

Step 1: Client browser sends an HTTP/1.1 connect method request toward the destination URL.

Client browser sends an HTTP/1.1 connect method request toward the destination URL.

Step 2: The connection request was interrupted by FortiProxy to challenge an HTTP/1.1 407 proxy authentication required with negotiate (Kerberos) authentication as a preferred method.

The connection request was interrupted by FortiProxy to challenge an HTTP/1.1 407 proxy authentication required with negotiate (Kerberos) authentication as a preferred method.

Step 3: Client browser responds to connect method request with a Kerberos service ticket (TGT) provided.

Client browser responds to connect method request with a Kerberos service ticket (TGT) provided.

Step 4: Fortiproxy to decipher the client Kerberos service ticket (TGT) with configured keytab to extract the user name used for LDAP query.

Fortiproxy to decipher the client Kerberos service ticket (TGT) with configured keytab to extract the user name used for LDAP query.

Step 5: FortiProxy to perform a proper lookup against the LDAP server for user and group membership matching.

FortiProxy to perform a proper lookup against the LDAP server for user and group membership matching.

Step 6: Authentication result showed success, the Fortiproxy allowed destination website access with an HTTP/1.1 200 OK.

Authentication result showed success, the Fortiproxy allowed destination website access with an HTTP/1.1 200 OK.

Alex Lim is a certified IT Technical Support Architect with over 15 years of experience in designing, implementing, and troubleshooting complex IT systems and networks. He has worked for leading IT companies, such as Microsoft, IBM, and Cisco, providing technical support and solutions to clients across various industries and sectors. Alex has a bachelor’s degree in computer science from the National University of Singapore and a master’s degree in information security from the Massachusetts Institute of Technology. He is also the author of several best-selling books on IT technical support, such as The IT Technical Support Handbook and Troubleshooting IT Systems and Networks. Alex lives in Bandar, Johore, Malaysia with his wife and two chilrdren. You can reach him at [email protected] or follow him on Website | Twitter | Facebook

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