Fix typos and improve clarity in documentation

Edit review per CI 3439

Author: przlplx

support/entra/entra-id/app-integration/troubleshoot-wif10201-no-validkey-securitytoken-mvc.md

@@ -1,6 +1,6 @@
 ---
-title: ASP.NET MVC application error WIF10201 No valid key mapping found for securityToken
-description: This article provides guidance for troubleshooting the the error "WIF10201- No valid key mapping found for securityToken".
+title: ASP.NET MVC Application Error WIF10201 No Valid Key Mapping Found for SecurityToken
+description: This article provides guidance for troubleshooting the error, "WIF10201- No valid key mapping found for securityToken."
 author: genlin
 ms.author: bachoang
 ms.service: entra-id
@@ -9,18 +9,18 @@ ms.date: 02/05/2025
 ms.custom: sap:Issues Signing In to Applications
 ---
 
-# WIF10201: No valid key mapping found for securityToken in ASP.NET application
+# "WIF10201: No valid key mapping found for securityToken" error in ASP.NET application
 
-This article provides guidance for troubleshooting an authentication issue in an ASP.NET MVC application that uses both [WS-Federation](https://github.com/Azure-Samples/active-directory-dotnet-webapp-wsfederation) OWIN middleware and [Windows Identity Foundation](../../../windows-server/user-profiles-and-logon/windows-identity-foundation.md) (WIF) to authenticate to Microsoft Entra ID.
+This article provides guidance for troubleshooting an authentication issue that occurs in an ASP.NET MVC application that uses both [WS-Federation](https://github.com/Azure-Samples/active-directory-dotnet-webapp-wsfederation) OWIN middleware and [Windows Identity Foundation](../../../windows-server/user-profiles-and-logon/windows-identity-foundation.md) (WIF) to authenticate to Microsoft Entra ID.
 
-## Symptom
+## Symptoms
 
-The ASP.NET MVC application was working previously. However, the following error is now occurring without any changes to the application.
+The ASP.NET MVC application that was previously working generates the following error message although no changes were made to the application:
 
 ```
 Error Details:
 Server Error in '/' Application.
-WIF10201: No valid key mapping found for securityToken: ‘System.IdentityModel.Tokens.X509SecurityToken' and issuer: 'https://sts.windows.net/<Directory ID>/'.
+WIF10201: No valid key mapping found for securityToken: 'System.IdentityModel.Tokens.X509SecurityToken' and issuer: 'https://sts.windows.net/<Directory ID>/'.
 
 Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
 
@@ -29,7 +29,7 @@ Exception Details: System.IdentityModel.Tokens.SecurityTokenValidationException:
 
 ## Cause
 
-Windows Identity Foundation uses the certificate thumbprint(s) in the web.config file as shown below to verify the signature of the token returned by the Entra ID upon a successful sign-in.
+To validate the signature of the token that's returned by the Entra ID after a successful sign-in, WIF uses the certificate thumbprints that are in the Web.config file, as shown in the following example:
 
 ```web.config
 <issuerNameRegistry type="System.IdentityModel.Tokens.ValidatingIssuerNameRegistry, 
@@ -47,10 +47,10 @@ System.IdentityModel.Tokens.ValidatingIssuerNameRegistry">
 </issuerNameRegistry>
 ```
 
-The error WIF10201 occurs when none of these certificate thumbprints match the one used by Entra ID to sign the token.
+The "WIF10201" error occurs if none of these certificate thumbprints match the one that's used by Entra ID to sign the token.
 
-The Entra ID uses a [signing key rollover mechanism](/entra/identity-platform/signing-key-rollover), which updates the certificate used to sign authentication tokens periodically. This key rollover causes the initial certificate thumbprints configured in the web.config file to become invalid, hence leading to the error.
+The Entra ID uses a [signing key rollover mechanism](/entra/identity-platform/signing-key-rollover) to update the certificate that's used to sign authentication tokens periodically. This key rollover causes the initial certificate thumbprints that are configured in the Web.config file to become invalid.
 
 ## Solution
 
-You can either update the certificate thumbprints in the web.config file manually or automate the process through code. For more information, see [Best practices for keys metadata caching and validation](/entra/identity-platform/signing-key-rollover#best-practices-for-keys-metadata-caching-and-validation).
+You can either manually update the certificate thumbprints that are in the Web.config file or automate the process through code. For more information, see [Best practices for keys metadata caching and validation](/entra/identity-platform/signing-key-rollover#best-practices-for-keys-metadata-caching-and-validation).