Add help to solve 431 errors with Azure Cloud (requarks#17)

* Add help to solve 431 errors with Azure Cloud

* Update azurewebapp.md

Co-authored-by: Jesper Kolbeck <[email protected]>
Co-authored-by: Nicolas Giard <[email protected]>

Author: 3 people

install/azurewebapp.md

@@ -74,4 +74,24 @@ We can now create the App Service where our wiki will run.
 1. Browse to your app public URL. *(Can be found in the **Overview** tab of your web app resource)*
 1. Follow the instructions to create the admin account and start using your wiki.
 
-![](https://a.icons8.com/cqaghpTd/Zi0crm/svg.svg){.align-abstopright}
+# 4. Troubleshooting
+
+## 4.1 431 Request Header Fields Too Large Issues 
+
+Enabling **App Service Authentication** in **Azure** might cause `Request Header Fields Too Large` errors.  
+To fix this:
+1. In your Azure Web App, navigate to **Configuration**.
+1. Add the following **Application Settings**:
+   ```
+   WEBSITE_AUTH_DISABLE_IDENTITY_FLOW: true
+   ```
+
+The issue can re-appear for graphql queries when enabling SAML 2.0 authentication in Wiki.js, even with above fix.  
+To solve that we need to increase the max header size for NodeJS.
+1. In your Azure Web App, navigate to **Configuration**.
+1. Add the following **Application Settings**:
+   ```
+   NODE_OPTIONS: --max-http-header-size=81920
+   ```
+
+![](https://a.icons8.com/cqaghpTd/Zi0crm/svg.svg){.align-abstopright}