Client Assertions

If your token client is using a client assertion instead of a shared secret, you can provide the assertion in two ways

• use the request parameter mechanism to pass a client assertion to the management
• implement the IClientAssertionService interface to centralize client assertion creation

Here’s a sample client assertion service using the Microsoft JWT library:

ClientAssertionService.cs

using Duende.AccessTokenManagement;
using Duende.IdentityModel;
using Duende.IdentityModel.Client;
using Microsoft.Extensions.Options;
using Microsoft.IdentityModel.JsonWebTokens;
using Microsoft.IdentityModel.Tokens;

public class ClientAssertionService(IOptionsSnapshot<ClientCredentialsClient> options)
    : IClientAssertionService
{
    public Task<ClientAssertion?> GetClientAssertionAsync(
      string? clientName = null, TokenRequestParameters? parameters = null)
    {
        if (clientName == "invoice")
        {
            var options1 = options.Get(clientName);

            var descriptor = new SecurityTokenDescriptor
            {
                Issuer = options1.ClientId,
                Audience = options1.TokenEndpoint,
                Expires = DateTime.UtcNow.AddMinutes(1),
                SigningCredentials = GetSigningCredential(),

                Claims = new Dictionary<string, object>
                {
                    { JwtClaimTypes.JwtId, Guid.NewGuid().ToString() },
                    { JwtClaimTypes.Subject, options1.ClientId! },
                    { JwtClaimTypes.IssuedAt, DateTime.UtcNow.ToEpochTime() }
                },

                AdditionalHeaderClaims = new Dictionary<string, object>
                {
                    { JwtClaimTypes.TokenType, "client-authentication+jwt" }
                }
            };

            var handler = new JsonWebTokenHandler();
            var jwt = handler.CreateToken(descriptor);

            return Task.FromResult<ClientAssertion?>(new ClientAssertion
            {
                Type = OidcConstants.ClientAssertionTypes.JwtBearer,
                Value = jwt
            });
        }

        return Task.FromResult<ClientAssertion?>(null);
    }

    private SigningCredentials GetSigningCredential()
    {
        throw new NotImplementedException();
    }
}