Slack Mutual TLS Recipe: Adding X-Client-Certificate-SAN header from client certificate
Problem this snippet solves:
The following is based on the documentation from Slack of how to authenticate requests from Slack via mutual TLS and pass along the information to a service that is not capable of mutual TLS via a X-Client-Certificate-SAN header.
Adapted from: https://api.slack.com/docs/verifying-requests-from-slack#mutual_tls
Based on question from: https://devcentral.f5.com/s/question/0D51T00006n6YltSAE/extract-san-from-client-ssl-certificate-insert-into-http-header
How to use this snippet:
Attach to Virtual Server that has both a HTTP and clientssl profile.
The clientssl profile must be configured for "require" or "request" to process the client certificate and use a CA certificate that verifies that it is a trusted certificate. The iRule will replace any headers that are sent by the client.
Code :
when HTTP_REQUEST {
if {[SSL::cert 0] ne ""}{
# extract SAN
set santemp [findstr [X509::extensions [SSL::cert 0]] "Subject Alternative Name" 32 ","]
# remove DNS: prefix
set san [findstr $santemp "DNS" 4]
# insert X-Client-Certificate-SAN header
HTTP::header replace X-Client-Certificate-SAN $san
} else {
HTTP::header remove X-Client-Certificate-SAN
}
}Tested this on version:
11.5
EmployeeEmployee3 Comments
MoQasemNimbostratus
I have similar setup but the requirement from app team is to extract cn from client certificate and insert it in http header what changes needed for this code?
- Eric_Chen
For the CN it would be the following.
when HTTP_REQUEST { if {[SSL::cert 0] ne ""}{ set tmpcn [X509::subject [SSL::cert 0]] set cn [findstr $tmpcn "CN=" 3] HTTP::header replace X-Client-Certificate-SAN $cn } else { HTTP::header remove X-Client-Certificate-SAN } } 
adidasn2022Hi Eric_Chen
Hope all is well.
I'm trying to create an rule whereby it extract the TLS cert DNS name and populate value into a new header field:
in x-forwarded-host-chkd.Is this easily done? Thanks
