Add new article on common JWT Bearer errors.

docs/en/Community-Articles/2025-04-20-IDX10204/POST.md

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+# Common errors in JWT Bearer
+
+When implementing JWT Bearer authentication in an ABP(tiered) application, you might occasionally encounter errors starting with `IDX`. These errors are related to JWT Bearer Token validation and this article will help you understand and resolve them.
+
+This article will introduce the principles of JWT Bearer authentication and provide some common error reasons and solutions.
+
+## Enable JWT Bearer authentication
+
+Your API project usually contains the following code, which enables JWT Bearer authentication and makes it as the default authentication scheme.
+
+We simply configure the JWT's `Authority` and `Audience` properties, and it will work fine.
+
+```csharp
+context.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+	.AddJwtBearer(options =>
+	{
+		options.Authority = "https://localhost:44301/"; //configuration["AuthServer:Authority"];
+		options.Audience = "MyProjectName";
+	});
+```
+
+> `AddJwtBearer` and `AddAbpJwtBearer` will do the same thing, but `AddAbpJwtBearer` is recommended.
+
+## JWT authentication process
+
+Let's take a look at how the above code works.
+
+A JWT Token usually consists of three parts: `Header`, `Payload`, and `Signature`.
+
+- `Header`: Contains the type and signing algorithm of the token
+- `Payload`: Contains the claims of the token, including `sub`, `aud`, `exp`, `iat`, `iss`, `jti`, `preferred_username`, `given_name`, `role`, `email`, etc.
+- `Signature`: The cryptographic signature of the token used to verify its authenticity
+
+Here is an example of a JWT Token issued by `AuthServer(OpenIddict)`:
+
+The `Header` part:
+
+![JWT Header](header.png)
+
+The `Payload` part:
+
+![JWT Payload](payload.png)
+
+### TokenValidationParameters
+
+In the `JwtBearerOptions`, there is a `TokenValidationParameters` property, which is used to validate the JWT Token.
+
+The default implementation for JWT Token validation is `JsonWebTokenHandler`, which comes from the [Microsoft.IdentityModel.JsonWebTokens](https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/) package.
+
+We didn't set the `TokenValidationParameters` property in the code above, so the default values below will be used:
+
+```csharp
+//...
+TokenValidationParameters.ValidateAudience = true
+TokenValidationParameters.ValidAudience = "MyProjectName"
+TokenValidationParameters.ValidAudiences = null
+
+TokenValidationParameters.ValidateIssuer = true
+TokenValidationParameters.ValidIssuer = null
+TokenValidationParameters.ValidIssuers = null
+//...
+```
+
+### JWT Bearer Token Validation Process
+
+During JWT Bearer authentication, API website will get the token from the HTTP request and validate it.
+
+The `JsonWebTokenHandler` will get the `OpenID Connect` metadata from the `AuthServer`, it will be used in the validation process, the current metadata request address is: https://localhost:44301/.well-known/openid-configuration , it is a fixed address calculated from the `Authority` property.
+
+First, the token's Signature is verified using the public key obtained from `OpenID Connect` metadata(https://localhost:44301/.well-known/jwks).
+
+Then, the payload is validated. The payload is a JSON object containing essential information such as the `token type`, `expiration time`, `issuer`, and `audience` etc.
+
+Most of the validation problems we may encounter are payload validation failures, for example:
+
+#### Lifetime
+
+If the token in your request has expired, the validation will fail. You will see the exception information like `IDX10230` in the log.
+
+#### Audience
+
+The `ValidAudience` of `TokenValidationParameters` is `MyProjectName`, the `aud` in the payload of the token is also `MyProjectName`, if the token does not contain `aud` or the `aud` does not match, the validation will fail. You may see the exception information like `IDX10206`, `IDX10277` or `IDX10208`.
+
+> If the `ValidateAudience` of `TokenValidationParameters` is `false`, then the `aud` will not be validated.
+
+#### Issuer
+
+The default value of `TokenValidationParameters.ValidateIssuer` is `true`, it requires the token's payload to contain the `issuer` field, and it must match one of `TokenValidationParameters.ValidIssuer` or `TokenValidationParameters.ValidIssuers`.
+
+> The default value of `ValidIssuer` or `ValidIssuers` is `null`, it will use the `issuer` from the `OpenID Connect` metadata as the default value.
+
+1. If the token's payload does not contain the `issuer` field, you may see the error `IDX10211`.
+2. If the API website cannot get the `OpenID Connect` metadata from AuthServer website, the validation will fail. You may see the error `IDX10204`, the full exception message is: `IDX10204: Unable to validate issuer. validationParameters.ValidIssuer is null or whitespace AND validationParameters.ValidIssuers is null or empty.`
+3. If the `issuer` does not match, the validation will fail. You may see the error `IDX10205` in the log.
+
+> If the `ValidateIssuer` of `TokenValidationParameters` is `false`, then the `issuer` will not be validated.
+
+> Please note that `OpenIddict` will use the current HTTP request information as the value of `issuer`. If the AuthServer website is deployed behind a reverse proxy or similar deployment configurations, the `issuer` in the token may not be the value you expect. In this case, please specify it manually.
+
+```csharp
+PreConfigure<OpenIddictServerBuilder>(serverBuilder =>
+{
+	serverBuilder.SetIssuer("https://localhost:44301/");
+});
+```
+
+## Troubleshooting
+
+To troubleshoot any `IDX` errors during JWT authentication, you can enable detailed logging by configuring the `identitymodel` logs as follows:
+
+```csharp
+using System.Diagnostics.Tracing;
+using Microsoft.IdentityModel.Logging;
+
+public class Program
+{
+    public async static Task<int> Main(string[] args)
+    {
+        IdentityModelEventSource.ShowPII = true;
+        IdentityModelEventSource.Logger.LogLevel = EventLevel.Verbose;
+        var wilsonTextLogger = newTextWriterEventListener("Logs/identitymodel.txt");
+        wilsonTextLogger.EnableEvents(IdentityModelEventSource.Logger, EventLevel.Verbose);
+
+		//...
+    }
+}
+```
+
+Additionally, you can enable `OpenIddict`'s `Verbose` logs for more detailed debugging information:
+
+```csharp
+var loggerConfiguration = new LoggerConfiguration()
+    .MinimumLevel.Debug()
+    .MinimumLevel.Override("Microsoft.EntityFrameworkCore", LogEventLevel.Warning)
+    .MinimumLevel.Override("OpenIddict", LogEventLevel.Verbose)
+    .Enrich.FromLogContext()
+    .WriteTo.Async(c => c.File("Logs/logs.txt"))
+```
+
+## Summary
+
+For JWT authentication, you need to pay attention to the following key points:
+
+1. Ensure your API website can communicate with the AuthServer properly
+2. Verify that the `aud` claim in your token matches the expected audience
+3. Confirm that the `issuer` claim in your token is valid and matches the configuration
+
+You can customize the `JwtBearerOptions`'s `TokenValidationParameters` to modify the validation rules to meet your actual needs.
+
+For example, if your `issuer` needs to support multiple subdomains, you can use the [Owl.TokenWildcardIssuerValidator](https://github.com/maliming/Owl.TokenWildcardIssuerValidator) library to customize the validation.
+
+```csharp
+services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
+    .AddJwtBearer(options =>
+    {
+        options.Authority = "https://abp.io";
+        options.Audience = "abp_io";
+
+        options.TokenValidationParameters.IssuerValidator = TokenWildcardIssuerValidator.IssuerValidator;
+        options.TokenValidationParameters.ValidIssuers = new[]
+        {
+            "https://{0}.abp.io"
+        };
+    });
+```
+
+## References
+
+- [JWT Authentication in ASP.NET Core](https://learn.microsoft.com/en-us/aspnet/core/security/authentication/jwt-auth?view=aspnetcore-8.0)
+- [OpenIddict](https://github.com/openiddict/openiddict-core)
+- [IdentityModel](https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet)
+- [Owl.TokenWildcardIssuerValidator](https://github.com/maliming/Owl.TokenWildcardIssuerValidator)