How can I validate a JWT token's signature in Logic Apps

1. Configure Authentication in Logic Apps:
- In your Logic App, go to the trigger settings and ensure that authentication is enabled. You can use the "IncludeAuthorizationHeadersInOutputs" option to include the JWT token in the trigger outputs[5].

2. Extract the JWT Token:
- Use the HTTP trigger to receive the JWT token. You can extract it from the Authorization header or a query parameter.

3. Validate the JWT Token:
- While Logic Apps doesn't directly validate JWT signatures within its built-in actions, you can use an external service or an Azure Function to validate the token.
- You can create an Azure Function that uses a library like `System.IdentityModel.Tokens.Jwt` to validate the JWT token's signature, issuer, audience, and expiration time[2][3].

4. Implement Signature Validation in Azure Function:
- In your Azure Function, use `JwtSecurityTokenHandler` to validate the token. You need to specify the validation parameters such as issuer, audience, and signing keys.
- Here’s a simplified example of how you might validate a token in C#:

csharp
   using System.IdentityModel.Tokens.Jwt;
   using Microsoft.IdentityModel.Tokens;

   public class JwtValidator
   {
       public bool ValidateJwtToken(string token, string issuer, string audience, string[] signingKeys)
       {
           var validationParams = new TokenValidationParameters
           {
               ValidateIssuer = true,
               ValidateAudience = true,
               ValidateLifetime = true,
               ValidateIssuerSigningKey = true,
               IssuerSigningKeys = signingKeys.Select(key => new SymmetricSecurityKey(Convert.FromBase64String(key))).ToList(),
               ValidIssuer = issuer,
               ValidAudience = audience
           };

           try
           {
               var handler = new JwtSecurityTokenHandler();
               handler.ValidateToken(token, validationParams, out _);
               return true;
           }
           catch (SecurityTokenValidationException)
           {
               return false;
           }
       }
   }
   

5. Integrate with Logic Apps:
- Call your Azure Function from your Logic App to validate the JWT token. If the validation succeeds, proceed with your workflow; otherwise, handle the error accordingly.

This approach allows you to leverage the capabilities of Azure Functions for complex token validation while still using Logic Apps for workflow management.

Citations:
[1] https://auth0.com/blog/how-to-validate-jwt-dotnet/
[2] https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/validate-an-identity-token
[3] https://www.criipto.com/blog/jwt-validation-guide
[4] https://stackoverflow.com/questions/49932596/ignore-jwt-bearer-token-signature-i-e-dont-validate-token
[5] https://autosysops.com/blog/parse-jwt-tokens-in-azure-logic-apps
[6] https://learn.microsoft.com/en-us/aspnet/core/security/authentication/configure-jwt-bearer-authentication?view=aspnetcore-9.0
[7] https://auth0.com/docs/secure/tokens/json-web-tokens/validate-json-web-tokens
[8] https://blog.logrocket.com/jwt-authentication-best-practices/
[9] https://learn.microsoft.com/en-us/azure/api-management/validate-jwt-policy
[10] https://www.cryptr.co/documentation/how-to-validate-jwt