jwt accomodation (#8126)

docs/examples/customization/jwt/README.md

@@ -0,0 +1,48 @@
+# Accommodation for JWT
+
+JWT (short for Json Web Token) is an authentication method widely used. Basically an authentication server generates
+a JWT and you then use this token in every request you make to a backend service. The JWT can be quite big and is
+present in every http headers. This means you may have to adapt the max-header size of your nginx-ingress in order
+to support it.
+
+## Symptoms
+
+If you use JWT and you get http 502 error from your ingress, it may be a sign that the buffer size is not big enough.
+
+To be 100% sure look at the logs of the `ingress-nginx-controller` pod, you should see something like this:
+
+```
+upstream sent too big header while reading response header from upstream...
+```
+
+
+## Increase buffer size for headers
+
+In nginx, we want to modify the property `proxy-buffer-size`. The size is arbitrary. It depends on your needs. Be aware
+that a high value can lower the performance of your ingress proxy. In general a value of 16k should get you covered.
+
+### Using helm
+If you're using helm you can simply use the [`config` properties](https://github.com/kubernetes/ingress-nginx/blob/main/charts/ingress-nginx/values.yaml#L37).
+```yaml
+ # -- Will add custom configuration options to Nginx https://kubernetes.github.io/ingress-nginx/user-guide/nginx-configuration/configmap/
+  config: 
+    proxy-buffer-size: 16k
+```
+
+## Manually in kubernetes config files
+
+If you use an already generated config from for a provider, you will have to change the `controller-configmap.yaml`
+
+```yaml
+---
+# Source: ingress-nginx/templates/controller-configmap.yaml
+apiVersion: v1
+kind: ConfigMap
+# ...
+data:
+  #...
+  proxy-buffer-size: "16k"
+```
+
+References:
+ * [Custom Configuration](../custom-configuration/)