How to get the detailed error in web api Authentication Failed scenario instead of "Message": "Authorization has been denied for this request."? - asp.net-web-api2

Question

I created a web api from VS template with a Values Controller decorated with [Authorize]. I have added Owin Startup as below:
[assembly: OwinStartup(typeof(WebAPIDotNet.Startup))]
namespace WebAPIDotNet
{
public class Startup
{
private static string clientId = "xxxxxxxxx"; // my actual client id from azure ad.
public void Configuration(IAppBuilder app)
{
app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions
{
AccessTokenFormat = new JwtFormat(
new TokenValidationParameters
{
// Check if the audience is intended to be this application
ValidAudiences = new[] { clientId, $"api://{clientId}" },
// Change below to 'true' if you want this Web API to accept tokens issued to one Azure AD tenant only (single-tenant)
// Note that this is a simplification for the quickstart here. You should validate the issuer. For details,
// see https://github.com/Azure-Samples/active-directory-dotnet-native-aspnetcore
ValidateIssuer = false,
}
//new OpenIdConnectSecurityTokenProvider("https://login.microsoftonline.com/common/v2.0/.well-known/openid-configuration")
),
AuthenticationMode = Microsoft.Owin.Security.AuthenticationMode.Active,
// Below Provider is just so that I can capture detailed errors while debugging, but no success
Provider = new OAuthBearerAuthenticationProvider
{
OnRequestToken = Onrequesttoken,
OnApplyChallenge = applyuingChallenge,
OnValidateIdentity = validatingidentiity
},
});
}
private Task validatingidentiity(OAuthValidateIdentityContext arg)
{
return Task.FromResult(0);
}
private Task applyuingChallenge(OAuthChallengeContext arg)
{
return Task.FromResult(0);
}
private Task Onrequesttoken(OAuthRequestTokenContext arg)
{
return Task.FromResult(0);
}
}
}
I have an access token already, and I have validated that it has the correct audience, etc. But making a GET request with Postman keeps giving me the msg - "Message": "Authorization has been denied for this request."
When i debug I can see the token as part of the Authorization, is there any way i can log/see actual error rather than "Message": "Authorization has been denied for this request." ?
Postman request:

Answer 1

Just in case someone else runs into this, I found the answer in Owin Katana docs. Essentially placing below config in your web.config will enable logs in the output window with details and I was able to see the underlying reason of failed authorization since I am using the Owin auth middleware.
<system.diagnostics>
<switches>
<add name="Microsoft.Owin" value="Verbose" />
</switches>
</system.diagnostics>