How to make a REST API request, with a certificate provided as String, in swift?

I have to make a POST request to an endpoint, where that request should be included with the client certificate. The problem here is, I receive the client certificate cert-chain as a string(the format as below).

Note: The string is much bigger :)

I tried to convert the string to NSData object and create a PKCS12 object. But converting to NSData itself fails.

How I converted is

let dataDecoded = Data(base64Encoded: certChainString, options: .ignoreUnknownCharacters)

This returns empty data object as the size of dataDecoded is 0 bytes.

How can I send the POST request with the certificate when the certChainString is provided?

Solution

Are you trying to convert it while it still includes -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----?

It isn't valid base64 with those included, so remove them first.

let certChainString = """
-----BEGIN CERTIFICATE-----

...

-----END CERTIFICATE-----
"""
let certString = certChainString
                      .replacingOccurrences(of: "-----BEGIN CERTIFICATE-----", with: "")
                      .replacingOccurrences(of: "-----END CERTIFICATE-----", with: "")

let dataDecoded  = Data(base64Encoded: certString, options: .ignoreUnknownCharacters)

If the API request returns important data, please consider reading more on Security topic first or use frameworks.

Edit:

import Foundation

let certChainString = """
-----BEGIN CERTIFICATE-----

... cert here ...

-----END CERTIFICATE-----
"""
let certString = certChainString
                      .replacingOccurrences(of: "-----BEGIN CERTIFICATE-----", with: "")
                      .replacingOccurrences(of: "-----END CERTIFICATE-----", with: "")

private var key: SecKey?

if let dataDecoded  = Data(base64Encoded: certString, options: .ignoreUnknownCharacters),
   let certificate = SecCertificateCreateWithData(nil, dataDecoded as CFData)
{
    var trust: SecTrust?
    let policy = SecPolicyCreateBasicX509()
    let status = SecTrustCreateWithCertificates(certificate, policy, &trust)

    if status == errSecSuccess, let trust {
        key = SecTrustCopyKey(trust)
    }
}

print(key)