Add a phase 7 on troubleshooting and error handling

[jmprieur]

Customers can be confused on how to debug web apps. Here we want to go through:

• the most frequent issues (not MFA etc … as it's already handled by the code in Microsoft.Identity.Web): bad client ID, bad secret, secret expired
• Troubleshooting guide

To help debugging the Web App and Web API you could enable:​

1. the IdentityModelExtension PII: See TodoListService/Startup.cs#L76

See also
https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/wiki/PII

// Since IdentityModel version 5.2.1 (or since Microsoft.AspNetCore.Authentication.JwtBearer version 2.2.0),​
// PII hiding in log files is enabled by default for GDPR concerns.​
// For debugging/development purposes, one can enable additional detail in exceptions by setting IdentityModelEventSource.ShowPII to true.​
Microsoft.IdentityModel.Logging.IdentityModelEventSource.ShowPII = true;​
```​
​
2. put breakpoints in the `JwtODICMiddlewareDiagnostics` class (or the `OJWTMiddlewareDiagnostics` class in the Web API)​
​
```CSharp​
// If you want to debug, or just understand the JwtBearer events, uncomment the following line of code​
options.Events = JwtBearerMiddlewareDiagnostics.Subscribe(options.Events);​
```​
​

[kalyankrishna1]

@kalyankrishna1 to check if we can accommodate in code gen