feat: Add endpoint returning tenant configured limits (#17101)

Author: salvacorts

Diff for: pkg/loki/config_handler.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"reflect"
 
+	"github.com/grafana/dskit/tenant"
 	"gopkg.in/yaml.v2"
 )
 
@@ -113,6 +114,29 @@ func configHandler(actualCfg interface{}, defaultCfg interface{}) http.HandlerFu
 	}
 }
 
+func (t *Loki) tenantLimitsHandler() func(http.ResponseWriter, *http.Request) {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if t.TenantLimits == nil {
+			http.Error(w, "Tenant configs not enabled", http.StatusNotFound)
+			return
+		}
+
+		user, _, err := tenant.ExtractTenantIDFromHTTPRequest(r)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusUnauthorized)
+			return
+		}
+
+		limit := t.TenantLimits.TenantLimits(user)
+		if limit == nil {
+			http.Error(w, "Tenant limits not found", http.StatusNotFound)
+			return
+		}
+
+		writeYAMLResponse(w, limit)
+	}
+}
+
 // writeYAMLResponse writes some YAML as a HTTP response.
 func writeYAMLResponse(w http.ResponseWriter, v interface{}) {
 	// There is not standardised content-type for YAML, text/plain ensures the

Diff for: pkg/loki/loki.go

@@ -11,10 +11,6 @@ import (
 	rt "runtime"
 	"time"
 
-	"go.uber.org/atomic"
-
-	"google.golang.org/grpc/health/grpc_health_v1"
-
 	"github.com/fatih/color"
 	"github.com/felixge/fgprof"
 	"github.com/go-kit/log/level"
@@ -30,6 +26,8 @@ import (
 	"github.com/grafana/dskit/signals"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
+	"go.uber.org/atomic"
+	"google.golang.org/grpc/health/grpc_health_v1"
 
 	"github.com/grafana/loki/v3/pkg/analytics"
 	blockbuilder "github.com/grafana/loki/v3/pkg/blockbuilder/builder"
@@ -505,6 +503,7 @@ func (t *Loki) bindConfigEndpoint(opts RunOpts) {
 		configEndpointHandlerFn = opts.CustomConfigEndpointHandlerFn
 	}
 	t.Server.HTTP.Path("/config").Methods("GET").HandlerFunc(configEndpointHandlerFn)
+	t.Server.HTTP.Path("/config/tenant/v1/limits").Methods("GET").HandlerFunc(t.tenantLimitsHandler())
 }
 
 // ListTargets prints a list of available user visible targets and their