Vapor JWT extension for parsing RSA keys from PEM, e.g. for Firebase Authentication

RSAKey+PEM.swift

extension RSAKey {
    init?(pem: String) {
        let bio = BIO_new(BIO_s_mem())
        defer {
            BIO_free(bio)
        }

        _ = pem.withCString { key in
            BIO_puts(bio, key)
        }

        guard let pkey = PEM_read_bio_PrivateKey(bio, nil, nil, nil) else {
            return nil
        }

        defer {
            EVP_PKEY_free(pkey)
        }
        
        guard let rsa = EVP_PKEY_get1_RSA(pkey) else {
            return nil
        }
        
        self = .private(rsa)
    }
}