Hello, I have an authentication flow where my app communicates with a backend protected by F5 client certificate validation. The client certificate is distributed via MDM and is available in the device keychain, but not accessible directly from the app. When using ASWebAuthenticationSession (or SFSafariViewController) Safari can successfully pick up and present the certificate during authentication, so that part works fine. However, the backend’s authenticate endpoint only supports a POST request with an Authorization header, whereas ASWebAuthenticationSession only accepts a GET URL when starting the session. My questions are: How is this type of flow typically implemented in iOS? Should the backend provide a GET-based endpoint that redirects into the POST, or is there a recommended iOS pattern (e.g., an intermediate HTML page that does the POST after certificate validation)? Are there Apple guidelines on handling certificate-based auth with ASWebAuthenticationSession when the API requires POST, especially for In-House distributed apps? Any guidance or best practices would be very helpful.

I am working on implementing mTLS authentication in my iOS app (Apple Inhouse & intune MAM managed app). The SCEP client certificate is deployed on the device via Intune MDM. When I try accessing the protected endpoint via SFSafariViewController/ASWebAuthenticationSession, the certificate picker appears and the request succeeds. However, from within my app (using URLSessionDelegate), the certificate is not found (errSecItemNotFound). The didReceive challenge method is called, but my SCEP certificate is not found in the app. The certificate is visible under Settings > Device Management > SCEP Certificate. How can I make my iOS app access and use the SCEP certificate (installed via Intune MDM) for mTLS requests? Do I need a special entitlement, keychain access group, or configuration in Intune or Developer account to allow my app to use the certificate? Here is the sample code I am using: final class KeychainCertificateDelegate: NSObject, URLSessionDelegate { func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) { guard challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodClientCertificate else { completionHandler(.performDefaultHandling, nil) return } // Get the DNs the server will accept guard let expectedDNs = challenge.protectionSpace.distinguishedNames else { completionHandler(.cancelAuthenticationChallenge, nil) return } var identityRefs: CFTypeRef? = nil let err = SecItemCopyMatching([ kSecClass: kSecClassIdentity, kSecMatchLimit: kSecMatchLimitAll, kSecMatchIssuers: expectedDNs, kSecReturnRef: true, ] as NSDictionary, &identityRefs) if err != errSecSuccess { completionHandler(.cancelAuthenticationChallenge, nil) return } guard let identities = identityRefs as? [SecIdentity], let identity = identities.first else { print("Identity list is empty") completionHandler(.cancelAuthenticationChallenge, nil) return } let credential = URLCredential(identity: identity, certificates: nil, persistence: .forSession) completionHandler(.useCredential, credential) } } func perform_mTLSRequest() { guard let url = URL(string: "https://sample.com/api/endpoint") else { return } var request = URLRequest(url: url) request.httpMethod = "POST" request.setValue("application/json", forHTTPHeaderField: "Accept") request.setValue("Bearer \(bearerToken)", forHTTPHeaderField: "Authorization") let delegate = KeychainCertificateDelegate() let session = URLSession(configuration: .ephemeral, delegate: delegate, delegateQueue: nil) let task = session.dataTask(with: request) { data, response, error in guard let httpResponse = response as? HTTPURLResponse, (200...299).contains(httpResponse.statusCode) else { print("Bad response") return } if let data = data { print(String(data: data, encoding: .utf8)!) } } task.resume() }