Just a snippet post to say that I've found a lighter (and imho preferable) way to configure Apache to accept client side SSL certificates (with regards to FOAF+SSL).
The Standard Way
This way essentially exports all SSL data, certs, client and server side if you read the notes has performance penalty.
SSLVerifyClient optional_no_ca
SSLVerifyDepth 1
SSLOptions +StdEnvVars
SSLOptions +ExportCertData
The Lighter Way
This way simply passes in the SSL_CLIENT_CERT in to the env REMOTE_USER and skips the rest which you don't use (for FOAF+SSL).
SSLVerifyClient optional_no_ca
SSLVerifyDepth 1
SSLUserName SSL_CLIENT_CERT
Tested and works very nicely (again, imho).
note: Enabling SSLOptions +FakeBasicAuth will overwrite this with the Subject from the client side certificate.
