example dotnet 6 code to sign an apple JWT from p8 certificate file

example.cs

public class TokenSigningRequest
{
    public string AppleTeamId { get; set; }
    public string AppleServiceId { get; set; }
    public string AppleKeyId { get; set; }
    public string P8key { get; set; }
}

[HttpPost]
public async Task<IActionResult> CreateSignedToken([FromBody, BindRequired] TokenSigningRequest requestBody)
{
    string audience = "https://appleid.apple.com";

    string issuer = requestBody?.AppleTeamId;
    string subject = requestBody?.AppleServiceId;
    string kid = requestBody?.AppleKeyId;
    string p8key = requestBody?.P8key;

    IList<Claim> claims = new List<Claim> {
        new Claim ("sub", subject)
    };
    using (ECDsa key = ECDsa.Create())
    {
        key.ImportPkcs8PrivateKey(Convert.FromBase64String(p8key), out _);

        // CngKey cngKey = CngKey.Import(Convert.FromBase64String(p8key), CngKeyBlobFormat.Pkcs8PrivateBlob);

        SigningCredentials signingCred = new SigningCredentials(
            new ECDsaSecurityKey(key),
            SecurityAlgorithms.EcdsaSha256
        );

        JwtSecurityToken token = new JwtSecurityToken(
            issuer,
            audience,
            claims,
            DateTime.Now,
            DateTime.Now.AddDays(180),
            signingCred
        );
        token.Header.Add("kid", kid);
        token.Header.Remove("typ");

        JwtSecurityTokenHandler tokenHandler = new JwtSecurityTokenHandler();

        string jwt = tokenHandler.WriteToken(token);

        return (ActionResult)new OkObjectResult(new
        {
            token = jwt
        });
    }
}