add header compatibility with prometheus

README.md

@@ -41,6 +41,8 @@ This will return metrics for all nodes. A query parameter to filter by host can
 - To use the Prometheus client, please configure environment variables `METRICS_PROVIDER_NAME`, `METRICS_PROVIDER_ADDRESS` and `METRICS_PROVIDER_TOKEN` to `Prometheus`, Prometheus address and auth token. Please do not set `METRICS_PROVIDER_TOKEN` if no authentication 
   is needed to access the Prometheus APIs. Default value of address set is `http://prometheus-k8s:9090` for Prometheus client.
 
+- To add custom headers for Prometheus authentication (e.g., OAuth bypass tokens), use the `METRICS_PROVIDER_HEADERS` environment variable with format `key1=value1,key2=value2`. Example: `METRICS_PROVIDER_HEADERS="X-Oauth-Bypass-Token=token123,X-API-Key=key456"`.
+
 - To use the SignalFx client, please configure environment variables `METRICS_PROVIDER_NAME`, `METRICS_PROVIDER_ADDRESS` and `METRICS_PROVIDER_TOKEN` to `SignalFx`, SignalFx address and auth token respectively. Default value of address set is `https://api.signalfx.com` for SignalFx client.
 
 ## Deploy `load-watcher` as a service

manifests/load-watcher-deployment.yaml

@@ -30,6 +30,8 @@ spec:
           value: [metrics_provider_endpoint]
         - name: METRICS_PROVIDER_TOKEN
           value: [token]
+        - name: METRICS_PROVIDER_HEADERS
+          value: "X-Oauth-Bypass-Token=token123"
         ports:
         - containerPort: 2020
 ---

pkg/watcher/internal/metricsprovider/prometheus.go

@@ -71,6 +71,25 @@ type promClient struct {
 	client api.Client
 }
 
+// customHeaderRoundTripper wraps an existing RoundTripper and adds custom headers
+type customHeaderRoundTripper struct {
+	headers map[string]string
+	rt      http.RoundTripper
+}
+
+// RoundTrip implements the RoundTripper interface
+func (c *customHeaderRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	// Clone the request to avoid modifying the original
+	req = req.Clone(req.Context())
+
+	// Add custom headers
+	for key, value := range c.headers {
+		req.Header.Set(key, value)
+	}
+
+	return c.rt.RoundTrip(req)
+}
+
 func loadCAFile(filepath string) (*x509.CertPool, error) {
 	caCert, err := ioutil.ReadFile(filepath)
 	if err != nil {
@@ -141,17 +160,31 @@ func NewPromClient(opts watcher.MetricsProviderOpts) (watcher.MetricsProviderCli
 		}
 	}
 
+	// Apply custom headers if provided
+	if len(opts.Headers) > 0 {
+		// Convert map[string]string to *config.Headers
+		configHeaders := &config.Headers{
+			Headers: make(map[string]config.Header),
+		}
+		for key, value := range opts.Headers {
+			configHeaders.Headers[key] = config.Header{
+				Values: []string{value},
+			}
+		}
+		roundTripper = config.NewHeadersRoundTripper(configHeaders, roundTripper)
+	}
+
+	// Apply auth token if provided
 	if promToken != "" {
-		client, err = api.NewClient(api.Config{
-			Address:      promAddress,
-			RoundTripper: config.NewAuthorizationCredentialsRoundTripper("Bearer", config.NewInlineSecret(opts.AuthToken), roundTripper),
-		})
-	} else {
-		client, err = api.NewClient(api.Config{
-			Address: promAddress,
-		})
+		roundTripper = config.NewAuthorizationCredentialsRoundTripper("Bearer", config.NewInlineSecret(opts.AuthToken), roundTripper)
 	}
 
+	// Create the client with the final round tripper
+	client, err = api.NewClient(api.Config{
+		Address:      promAddress,
+		RoundTripper: roundTripper,
+	})
+
 	if err != nil {
 		log.Errorf("error creating prometheus client: %v", err)
 		return nil, err

pkg/watcher/metricsprovider.go

@@ -32,12 +32,44 @@ const (
 	MetricsProviderTokenKey   = "METRICS_PROVIDER_TOKEN"
 	MetricsProviderAppKey     = "METRICS_PROVIDER_APP_KEY"
 	InsecureSkipVerify        = "INSECURE_SKIP_VERIFY"
+	MetricsProviderHeadersKey = "METRICS_PROVIDER_HEADERS"
 )
 
 var (
 	EnvMetricProviderOpts MetricsProviderOpts
 )
 
+// parseHeadersFromEnv parses headers from environment variable
+// Expected format: "key1=value1,key2=value2,key3=value3"
+// Example: "http_x_oauth_bypass_token=token123,X-API-Key=key456"
+func parseHeadersFromEnv(headersEnv string) map[string]string {
+	headers := make(map[string]string)
+	if headersEnv == "" {
+		return headers
+	}
+
+	// Split by comma to get individual header pairs
+	headerPairs := strings.Split(headersEnv, ",")
+	for _, pair := range headerPairs {
+		pair = strings.TrimSpace(pair)
+		if pair == "" {
+			continue
+		}
+
+		// Split by = to get key and value
+		parts := strings.SplitN(pair, "=", 2)
+		if len(parts) == 2 {
+			key := strings.TrimSpace(parts[0])
+			value := strings.TrimSpace(parts[1])
+			if key != "" && value != "" {
+				headers[key] = value
+			}
+		}
+	}
+
+	return headers
+}
+
 func init() {
 	var ok bool
 	EnvMetricProviderOpts.Name, ok = os.LookupEnv(MetricsProviderNameKey)
@@ -53,6 +85,10 @@ func init() {
 	} else {
 		EnvMetricProviderOpts.InsecureSkipVerify = false
 	}
+
+	// Parse headers from environment variable
+	headersEnv, _ := os.LookupEnv(MetricsProviderHeadersKey)
+	EnvMetricProviderOpts.Headers = parseHeadersFromEnv(headersEnv)
 }
 
 // Interface to be implemented by any metrics provider client to interact with Watcher
@@ -75,4 +111,5 @@ type MetricsProviderOpts struct {
 	AuthToken          string
 	ApplicationKey     string
 	InsecureSkipVerify bool
+	Headers            map[string]string
 }