Using `SecCodeCopyGuestWithAttributes` with auditToken results in `100001 - UNIX[Operation not permitted]`

Hi everyone :)

I'm exploring XPC these days; more specifically, I'm trying to establish a connection between a macOS application and an XPC service. I succeeded in establishing the connection, but now I'm trying to verify the incoming connection by using SecCodeCopyGuestWithAttributes, passing it an audit token.

But I got the following error:

2024-01-18 10:43:06.805435+0100 DemoService[1627:7118397] [logging-persist] cannot open file at line 46922 of [554764a6e7]
2024-01-18 10:43:06.805452+0100 DemoService[1627:7118397] [logging-persist] os_unix.c:46922: (0) open(/private/var/db/DetachedSignatures) - Undefined error: 0
Cannot get SecCode: 100001 - UNIX[Operation not permitted]
Audit token: Optional(32 bytes)

The last two lines come from my code:

class XPCClientValidator {
    var secCodeOptional: SecCode? = nil;
    
    func identifyGuest(for connection: NSXPCConnection) -> Bool {
        let auditToken = AuditToken.extractToken(from: connection)
        let hostSecCode: SecCode? = nil; // This is a way to indicate that the code signing root of trust hould be used as host.
        let attributes = [ kSecGuestAttributeAudit: auditToken ] as CFDictionary
        let secFlags = SecCSFlags(rawValue: 0)
        
        // Asks a code host to identify the guest given the audit token
        let status: OSStatus = SecCodeCopyGuestWithAttributes(hostSecCode, attributes, secFlags, &self.secCodeOptional)
        if (status != errSecSuccess) {
            let msg = SecCopyErrorMessageString(status, nil)!
            print("Cannot get SecCode: \(status) - \(msg)")
            print("Audit token: \(String(describing: auditToken))")
            return false
        }
        
        guard let _ = secCodeOptional else {
            NSLog("Couldn't unwrap the secCode")
            return false
        }
        
        return true
    }
}

I saw a few posts on the forum, but nothing helped me to solve this issue.

The complete source code is here: https://github.com/tony-go/XPCDemo/tree/secure-xpc

Note: If you want to reproduce it, you have to:

• start the app
• type a random input
• click on "uppercase it"