Web Authentication Nuts and Bolts: “Authentication Appliance”

Web Authentication Nuts and Bolts:“Authentication Appliance” EDUCAUSE Dartmouth PKI Deployment Summit 7/27/2005 Presented by: Mark Franklin Dartmouth College PKI Lab Mark.J.Franklin@Dartmouth.EDU

Background Dartmouth’s Oracle-based web applications allow end user PKI authentication Anticipated 12,000 pre-matriculated students checking acceptance status all at once Too much HTTPS/SSL traffic for our Oracle application servers Needed more SSL capacity to avoid a meltdown Selected F5 load balancer/SSL termination appliance

The Problem • PKI authentication happens where SSL is terminated • Used to be in Oracle application server • Now in F5 appliance • Thus, Oracle app server doesn’t have knowledge of authentication Impending doom for our PKI authentication! (queue ominous music)

Original Configuration

The Solution • F5 supports end user PKI authentication • Validate user’s certificate (inc. revocation) • At this point, we have verified user’s identity • Insert custom HTTP headers to pass authentication information to the application server

New Configuration

Security Assumptions • F5 appliance properly verifies certificates (we tested to confirm this) • No alternate route to app servers (users could spoof custom headers) • Network from F5 to app servers is secure (it’s in our computer room) • F5 box is secure (we’re trusting it to do our authentication) • F5 logic eliminates any inbound custom authn headers (we programmed this)

Implementation • Configured SSL normally on F5 • Turned on standard F5 client-side PKI authn • Added iRule (TCL) logic in F5 to insert custom headers for users with PKI credentials • Modified Oracle app server authn logic (PL/SQL) to accept custom headers as valid authn & retrieve user info from them

iRule Logic to Reject Invalid Cert when CLIENTSSL_CLIENTCERT { if { [SSL::verify_result] } { log LOCAL0.warn "Client cert didn't verify, openssl code=[SSL::verify_result]" reject } }

when HTTP_REQUEST { # Eliminate any inbound spoofed authentication headers while {[HTTP::header exists F5PKI_CN]} { HTTP::header remove F5PKI_CN log LOCAL0.warn "removed inbound F5PKI_CN header - possible attack" } if { [SSL::cert count] != 0 } { # User authenticated with PKI, so get PKI DN set subject { } lappend subject [X509::subject [SSL::cert 0]] # Parse out the DN fields we need and set outbound header values foreach entry [ split $subject / ] { foreach {name value} [ split $entry = ] { switch $name { CN { HTTP::header replace F5PKI_CN $value } OU { HTTP::header replace F5PKI_OU $value } UID { HTTP::header replace F5PKI_UID $value } } } } } } iRule Logic for Custom Headers

Gotchas • F5 appliance is complex, takes a while to configure (even without PKI) • F5 by default doesn’t reject authentication using expired or revoked certificates, need to explicitly check for invalid certs and use iRule command to reject the authentication • Had to learn TCL for iRules (not too bad, and it’s extremely powerful) • F5 uses lots of server ID certs (one for each service), we found it useful to get a *.dartmouth.edu cert (from Verisign in order to appease Oracle Java applets)

Gotchas 2 • Internet Explorer has issues with SSL, especially with client-side PKI: • Apache turns off a bunch of stuff when it detects IE (including SSL session persistence) • Lots of experimenting to get SSL profile settings to accommodate IE with client-side PKI: • No SSL persistence cache • Long alert, handshake timeouts (10,000 seconds) • Long renegotiate period (10,000 seconds) • Renegotiate size indefinite, renegotiate max record delay huge (429496729 records) • Unclean shutdown not checked, strict resume checked

Conclusions • Disadvantages: • F5 appliance is expensive, but we needed it anyway for SSL bandwidth and load balancing • Advantages: • No client-side PKI on web server • Implement PKI authentication for any web server without special software or configurations • Only F5 admin needs to deal with PKI at all • Custom headers easy to parse in web applications • F5 appliance working very well, bandwidth to spare • Cost-effective way to offload SSL processing We now have a “PKI authentication appliance”.

Web Authentication Nuts and Bolts: “Authentication Appliance”