feat: add new prometheus metrics endpoint #672 (#673)

Adds endpoint `/metrics` for prometheus metrics collection to the Admin API Endpoint.

Closes #672

.schema/api.swagger.json

@@ -320,6 +320,24 @@
         }
       }
     },
+    "/metrics/prometheus": {
+      "get": {
+        "description": "```\nmetadata:\nannotations:\nprometheus.io/port: \"4445\"\nprometheus.io/path: \"/metrics/prometheus\"\n```",
+        "produces": [
+          "plain/text"
+        ],
+        "tags": [
+          "admin"
+        ],
+        "summary": "Get snapshot metrics from the Hydra service. If you're using k8s, you can then add annotations to\nyour deployment like so:",
+        "operationId": "prometheus",
+        "responses": {
+          "200": {
+            "description": "Empty responses are sent when, for example, resources are deleted. The HTTP status code for empty responses is\ntypically 201."
+          }
+        }
+      }
+    },
     "/recovery/link": {
       "post": {
         "description": "This endpoint creates a recovery link which should be given to the user in order for them to recover\n(or activate) their account.",

cmd/daemon/serve.go

@@ -5,6 +5,8 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/ory/kratos/metrics/prometheus"
+
 	"github.com/ory/analytics-go/v4"
 
 	"github.com/ory/x/flagx"
@@ -84,6 +86,7 @@ func serveAdmin(d driver.Driver, wg *sync.WaitGroup, cmd *cobra.Command, args []
 	r.RegisterAdminRoutes(router)
 	n.Use(NewNegroniLoggerMiddleware(l, "admin#"+c.SelfAdminURL().String()))
 	n.Use(sqa(cmd, d))
+	n.Use(d.Registry().PrometheusManager())
 
 	if tracer := d.Registry().Tracer(); tracer.IsLoaded() {
 		n.Use(tracer)
@@ -144,6 +147,7 @@ func sqa(cmd *cobra.Command, d driver.Driver) *metricsx.Service {
 				strings.ReplaceAll(verification.PublicVerificationInitPath, ":via", "email"),
 				verification.PublicVerificationRequestPath,
 				errorx.ErrorsPath,
+				prometheus.MetricsPrometheusPath,
 			},
 			BuildVersion: d.Registry().BuildVersion(),
 			BuildHash:    d.Registry().BuildHash(),

docs/docs/admin/managing-users-identities.mdx

@@ -74,6 +74,7 @@ To create the account recovery link, use:
   ]}>
 <TabItem value="curl">
 
+
 ```shell script
 $ curl --request POST -sL \
     --header "Content-Type: application/json" \
@@ -93,6 +94,7 @@ $ curl --request POST -sL \
 </TabItem>
 <TabItem value="go">
 
+
 ```go
 package main
 
@@ -143,6 +145,7 @@ email, this feature is tracked as
 </TabItem>
 </Tabs>
 
+
 ### Import a User Identity
 
 This feature is not implemented yet.