Generate X.509 certificate (and public/private key) in Swift iOS

Question

I want to generate a public/private key along with a certificate. I want to send this certificate to the server for future validation. I am able to generate the public and private key using SecKeyCreateRandomKey and SecKeyCopyPublicKey. I have also created an external representation of the key using SecKeyCopyExternalRepresentation, which is in DER format. I am stuck on how to create a self signed X.509 certificate from this.

Something similar to this on Android: keyStore.getCertificate()

let tag = "com.example.keys.test".data(using: .utf8)!
let attributes: [String: Any] =
            [kSecAttrKeyType as String: kSecAttrKeyTypeRSA,
             kSecAttrKeySizeInBits as String:      2048,
             kSecPrivateKeyAttrs as String:
                [kSecAttrIsPermanent as String:    true,
                 kSecAttrApplicationTag as String: tag]
        ]
var error: Unmanaged<CFError>?
let privateKey = SecKeyCreateRandomKey(attributes as CFDictionary, &error)
let publicKey = SecKeyCopyPublicKey(privateKey!)
let publicKeyData = SecKeyCopyExternalRepresentation(publicKey!, &error)! as Data