If Apache is in use as a ReverseProxy, it can be used to add additional headers.

Alternately APIX-G can add headers using a transformation or a Full-type Mapping.
Using a stylesheet has additional flexibility of setting conditions to look into the NB Request context as well.

 

All Supported Platforms

#viaAPIX
By using a Transformation, APIX can add additional headers to the outgoing/southbound request it sends to the Target.
Please see attached archive for a sample stylesheets
-- this should be configured as a Full-type Mapping and applied as a Request Transform on the Target.

#viaApache
Using the "RequestHeader" directives Apache can add headers to outgoing request it forwards to the Target, when setup as ReverseProxy.
Here is the one I tested with:
------------
ProxyPass /viaApache/ http://vviswana-hpz2:9222/
ProxyPassReverse /viaApache/ http://vviswana-hpz2:9222/

<Location /viaApache >
#    RequestHeader add X-SSL_PROTOCOL "%{SSL_PROTOCOL}s"
#    RequestHeader add CAIssuer "%{SSL_CLIENT_I_DN}s"
#    RequestHeader add SerialNumber "%{SSL_CLIENT_S_DN}s"
#    RequestHeader add partial_SerialNumber "%{SSL_CLIENT_S_DN_CN}s"
#    RequestHeader add full_SerialNumber "%{SSL_CLIENT_S_DN}s"
RequestHeader add APIKey_Apache "dummyAPIKey-via-apache"
</Location>
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Please refer to Apache docs for more informatio on this.

Also attached is a sample debug enabled log showing the above options in play.

Note: The below command can be used to validate the stylesheet before testing on the engine:
java -cp C:/apix233/asg/2.3/lib/asg-functions.jar;C:/apix233/asg/2.3/lib/ext/tpcl/saxon9pe.jar;C:/apix233/asg/2.3/lib/ext/tpcl/json_simple-1.1.jar;C:/apix233/be/5.2/lib/ext/tibco/TIBCOxml.jar;C:/apix233/asg/2.3/lib/ext/tpcl/log4j-1.2.15.jar;C:/apix233/be/5.2/lib/ext/tpcl/apache/commons-lang3-3.3.2.jar;C:/apix233/be/5.2/lib/cep-common.jar;C:/apix233/be/5.2/lib/cep-kernel.jar;C:/apix233/asg/2.3/lib/ext/tpcl/merastring2base64.jar  com.tibco.be.functions.xml.XsltTransformer ./

This article provides inputs and sample for adding additional headers to the SB HTTP Request.