using var cert = new CertificateBuilder().Create();

//A public & private keypair must be created first, outside of the CertificateBuilder, otherwise you'd have no way to retrieve the private-key used for the new CertificateSigningRequest object
using var keys = RSA.Create();

//Creating a CertificateSigningRequest
var csr = new CertificateBuilder()
    .SetUsage(CertificateUsage.Server)
    .SetSubject(b => b.SetCommonName("*.fake.domain"))
    .SetDnsNames("*.fake.domain", "fake.domain")
    .SetKeyPair(keys)
    .CreateCertificateSigningRequest();

//The CertificateRequest object is accessible here:
var certRequest = csr.CertificateRequest;

//CSR can be exported to a string
Console.WriteLine(csr.ToPemString());

//Or to a file or StringWriter instance
csr.ExportAsPem("csr.pem");

//Using a fluent style
using var cert = new CertificateBuilder()
    .SetUsage(CertificateUsage.Server)
    .SetFriendlyName("Example self-signed web-server certificate")
    .SetSubject(b => b.SetCommonName("*.fake.domain"))
    .SetDnsNames("*.fake.domain", "fake.domain")
    .SetNotAfter(DateTimeOffset.UtcNow.AddMonths(1))
    .Create();

//And just to demonstrate using object initializers (I'll use fluent style from now on though)
using var builder = new CertificateBuilder() {
    Usage = CertificateUsage.Server,
    FriendlyName = "Example self-signed web-server certificate",
    Subject = new X500NameBuilder().SetCommonName("*.fake.domain"),
    DnsNames = new[] { "*.fake.domain", "fake.domain" },
    NotAfter = DateTimeOffset.UtcNow.AddMonths(1)
};
var cert = builder.Create();

//A CA's expiry date must be later than that of any certificates it will issue
using var issuer = new CertificateBuilder()
    .SetUsage(CertificateUsage.CA)
    .SetFriendlyName("Example root CA")
    .SetSubject(b => b.SetCommonName("Example root CA"))
    .SetNotAfter(DateTimeOffset.UtcNow.AddYears(100))
    .Create();

//Note: the 'issuer' certificate used must have a private-key attached in order to sign this new certificate
using var cert = new CertificateBuilder()
    .SetUsage(CertificateUsage.Client)
    .SetFriendlyName("Example client-auth certificate")
    .SetSubject(b => b.SetCommonName("User: Michael"))
    .SetNotAfter(DateTimeOffset.UtcNow.AddYears(1))
    .SetIssuer(issuer)
    .Create();

using var cert = new CertificateBuilder()
    .SetFriendlyName("Example certificate with customized extensions")
    .SetSubject(b => b.SetCommonName("Example certificate with customized extensions"))
    .AddExtension(new X509BasicConstraintsExtension(false, false, 0, true))
    .AddExtension(new X509KeyUsageExtension(X509KeyUsageFlags.DigitalSignature | X509KeyUsageFlags.KeyEncipherment | X509KeyUsageFlags.DataEncipherment, true))
    .AddExtension(new X509EnhancedKeyUsageExtension(new OidCollection { new(KeyPurposeID.AnyExtendedKeyUsage.Id) }, false))
    .SetIssuer(issuer)
    .Create();