include documentation about the httpOption annotation (#4273)

* include documentation about the httpOption annotation

* drop trailing whitespace

* pr feedback

config/nav.yml

@@ -72,6 +72,7 @@ nav:
             - Configuring custom domains: developer/serving/services/custom-domains.md
             - Using a custom TLS certificate for DomainMapping: developer/serving/services/byo-certificate.md
             - Configure resource requests and limits: developer/serving/services/configure-requests-limits-services.md
+            - HTTPS redirection: developer/serving/services/http-option.md
           - Traffic management: developer/serving/traffic-management.md
           - Configuring gradual rollout of traffic to Revisions: developer/serving/rolling-out-latest-revision.md
           - Deploying from private registries: developer/serving/deploying-from-private-registry.md

docs/developer/serving/services/http-option.md

@@ -0,0 +1,24 @@
+# HTTPS redirection
+
+Operators can force HTTPS redirection for all Services. See the `httpProtocol` mentioned in the [Turn on AutoTLS](../../../serving/using-auto-tls.md) page for more details.
+
+### Overriding the default HTTP behaviour
+
+You can override the default behavior for each Service by configuring the `networking.knative.dev/httpOption` annotation:
+
+```yaml
+apiVersion: serving.knative.dev/v1
+kind: Service
+metadata:
+  name: example
+  namespace: default
+  annotations:
+    networking.knative.dev/httpOption: "enabled"
+spec:
+...
+```
+
+The possible values are:
+
+ - `enabled` - Services will accept HTTP traffic
+ - `redirected` - Services send a 301 redirect for all HTTP connections and ask clients to use HTTPS instead