Supporting multiple JWA and ES256 in ASP.​NET Core JWT bearer authentication

JwtBearerMultipleJwaExtensions.cs

using System;
using System.Text;
using System.Security.Cryptography;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;

namespace Microsoft.Extensions.DependencyInjection
{
    public static class JwtBearerMultipleJwaExtensions
    {
        public static AuthenticationBuilder AddJwtBearerWithHs256AndEs256(this AuthenticationBuilder builder, string hs256Key, string es256PublicKey, Action<JwtBearerOptions> configureOptions)
        {
            return builder.AddJwtBearer(options =>
            {
                configureOptions(options);
                options.TokenValidationParameters.IssuerSigningKeys = new SecurityKey[]
                {
                    GetHS256IssuerSigningKey(hs256Key),
                    GetES256IssuerSigningKey(es256PublicKey)
                };
            });
        }

        private static SecurityKey GetHS256IssuerSigningKey(string hs256Key)
        {
            return new SymmetricSecurityKey(Encoding.UTF8.GetBytes(hs256Key));
        }

        private static SecurityKey GetES256IssuerSigningKey(string es256PublicKey)
        {
            Span<byte> decodedPublicKey = FromUrlBase64String(es256PublicKey);

            return new ECDsaSecurityKey(ECDsa.Create(new ECParameters
            {
                Curve = ECCurve.NamedCurves.nistP256,
                Q = new ECPoint
                {
                    X = decodedPublicKey.Slice(1, 32).ToArray(),
                    Y = decodedPublicKey.Slice(33).ToArray()
                }
            }));

        }

        private static byte[] FromUrlBase64String(string input)
        {
            input = input.Replace('-', '+').Replace('_', '/');

            while (input.Length % 4 != 0)
            {
                input += "=";
            }

            return Convert.FromBase64String(input);
        }
    }
}

Startup.cs

public class Startup
{
    private const string JWT_HS256_KEY = "GRQKzLUn9w59LpXEbsESa8gtJnN3hyspq7EV4J6Fz3FjBk994r";
    private const string JWT_ES256_PUBLIC_KEY = "BK5sn4jfa0Jqo9MhV01oyzK2FaEHm0KqkSCuUkKr53-9cr-vBE1a9TiiBaWy7hy0eOUF1jhZnwcd3vof4wnwSw0";

    ...

    public void ConfigureServices(IServiceCollection services)
    {
        ...

        services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme).AddJwtBearerWithHs256AndEs256(JWT_HS256_KEY, JWT_ES256_PUBLIC_KEY, options =>
        {
            ...
        });

        ...
    }

    ...
}