How to handle custom claims in an Open ID Connect-authenticated ASP.NET Core app

Today, I learned how to handle custom claims in an Open ID Connect authenticated ASP.NET Core app.

The scenario goes like this. I have an ASP.NET Core app that authenticates with Open Id Connect. It receives a bearer token from the authentication server. Besides OIDC claims, this token has been forged with additional custom claims for use in the app. However, only ODIC claims exist when I parse HttpContext.User.Identity.Claims in my middleware. If I retrieve the token with HttpContext.GetTokenAsync and decode it, I confirm it contains all the claims I need. Where have my custom claims gone? Or, how can I get User.Identity to provide them along with the OIDC ones?

As it turns out, one must hack them into the User.Identity.Claims collection by hand. That’s done by leveraging the OnTokenValidated event handler like this:

authenticationBuilder.AddOpenIdConnect("oidc", options =>
{
    options.Authority = "authority";
    options.ClientId = "client_id";
    options.ClientSecret = "secret";
    options.ResponseType = "code";

    ...
    options.GetClaimsFromUserInfoEndpoint = true;
    options.SaveTokens = true;
    options.Events = new()
    {
        OnTokenValidated = context =>
        {
            // adds custom claims from the token into Principal.Identity
            if (context.Principal?.Identity is not ClaimsIdentity claimsIdentity) return Task.CompletedTask;
            
            var accessToken = context.TokenEndpointResponse?.AccessToken;
            if (string.IsNullOrEmpty(accessToken)) return Task.CompletedTask;
            
            var handler = new JwtSecurityTokenHandler();
            if (handler.ReadToken(accessToken) is not JwtSecurityToken jsonToken) return Task.CompletedTask;
            
            foreach (var claim in jsonToken.Claims)
                if (claimsIdentity.Claims.All(c => c.Type != claim.Type))
                    claimsIdentity.AddClaim(claim);

            return Task.CompletedTask;
        }
    };
});

Is there a better and less hacky way to achieve the same result? Please let me know.