module/prometheus: add bearer_token_file option (#431)

config/go.d/prometheus.conf

@@ -92,6 +92,12 @@
 #    Syntax:
 #      max_time_series: 1000
 #
+#
+#  - bearer_token_file
+#    Path to bearer token file.
+#    Syntax:
+#      bearer_token_file: '/var/run/secrets/kubernetes.io/serviceaccount/token'
+#
 #  - username
 #    Username for basic HTTP authentication.
 #    Syntax:

modules/prometheus/init.go

@@ -3,6 +3,7 @@ package prometheus
 import (
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"strings"
 
 	"github.com/netdata/go.d.plugin/pkg/prometheus"
@@ -25,15 +26,24 @@ func (p Prometheus) initPrometheusClient() (prometheus.Prometheus, error) {
 		return nil, fmt.Errorf("creating HTTP client: %v", err)
 	}
 
+	req := p.Request.Copy()
+	if p.BearerTokenFile != "" {
+		token, err := ioutil.ReadFile(p.BearerTokenFile)
+		if err != nil {
+			return nil, fmt.Errorf("reading bearer token file: %v", err)
+		}
+		req.Headers["Authorization"] = "Bearer " + string(token)
+	}
+
 	sr, err := p.Selector.Parse()
 	if err != nil {
 		return nil, fmt.Errorf("parsing selector: %v", err)
 	}
 
 	if sr != nil {
-		return prometheus.NewWithSelector(client, p.Request, sr), nil
+		return prometheus.NewWithSelector(client, req, sr), nil
 	}
-	return prometheus.New(client, p.Request), nil
+	return prometheus.New(client, req), nil
 }
 
 func (p Prometheus) initOptionalGrouping() ([]optionalGrouping, error) {

modules/prometheus/prometheus.go

@@ -41,11 +41,12 @@ func New() *Prometheus {
 
 type (
 	Config struct {
-		web.HTTP       `yaml:",inline"`
-		MaxTS          int           `yaml:"max_time_series"`
-		MaxTSPerMetric int           `yaml:"max_time_series_per_metric"`
-		Selector       selector.Expr `yaml:"selector"`
-		Grouping       []GroupOption `yaml:"group"`
+		web.HTTP        `yaml:",inline"`
+		BearerTokenFile string        `yaml:"bearer_token_file"` // TODO: part of web.Request?
+		MaxTS           int           `yaml:"max_time_series"`
+		MaxTSPerMetric  int           `yaml:"max_time_series_per_metric"`
+		Selector        selector.Expr `yaml:"selector"`
+		Grouping        []GroupOption `yaml:"group"`
 	}
 	GroupOption struct {
 		Selector string `yaml:"selector"`