feat: make it possible to read secrets from files

changelog/unreleased/file-secrets.md

@@ -0,0 +1,12 @@
+Change: Read secrets form files
+
+We have added proper support to load secrets like the token or the private key
+for app authentication from files or from base64-encoded strings. Just provide
+the flags or environment variables for token or private key with a DSN formatted
+string like `file://path/to/file` or `base64://Zm9vYmFy`.
+
+Since the private key for GitHub App authentication had been provided in
+base64-encoded format this is a breaking change as this won't work anymore until
+you prefix the value with `base64://`.
+
+https://github.com/promhippie/github_exporter/pull/245

docs/content/usage.md

@@ -98,6 +98,27 @@ directly at [http://localhost:9504/metrics](http://localhost:9504/metrics):
       - GITHUB_EXPORTER_REPO=promhippie/example
 {{< / highlight >}}
 
+It's also possible to provide the token to access the GitHub API gets provided
+by a file, in case you are using some kind of secret provider. For this use case
+you can write the token to a file on any path and reference it with the
+following format:
+
+{{< highlight diff >}}
+  github-exporter:
+    image: promhippie/github-exporter:latest
+    restart: always
+    environment:
+-     - GITHUB_EXPORTER_TOKEN=bldyecdtysdahs76ygtbw51w3oeo6a4cvjwoitmb
++     - GITHUB_EXPORTER_TOKEN=file://path/to/secret/file/with/token
+      - GITHUB_EXPORTER_LOG_PRETTY=true
+      - GITHUB_EXPORTER_ORG=promhippie
+      - GITHUB_EXPORTER_REPO=promhippie/example
+{{< / highlight >}}
+
+Besides the `file://` format we currently also support `base64://` which expects
+the token in a base64 encoded format. This functionality can be used for the
+token and the private key for GitHub App authentication so far.
+
 If you want to collect the metrics of all repositories within an organization
 you are able to use globbing, but be aware that all repositories matched by
 globbing won't provide metrics for the number of subscribers, the number of

pkg/action/helper.go

@@ -0,0 +1,16 @@
+package action
+
+// boolP returns a boolean pointer.
+func boolP(i bool) *bool {
+	return &i
+}
+
+// stringP returns a string pointer.
+func stringP(i string) *string {
+	return &i
+}
+
+// slceP returns a slice pointer.
+func sliceP(i []string) *[]string {
+	return &i
+}

pkg/action/server.go

@@ -3,7 +3,6 @@ package action
 import (
 	"context"
 	"crypto/tls"
-	"encoding/base64"
 	"io"
 	"net/http"
 	"os"
@@ -233,30 +232,6 @@ func handler(cfg *config.Config, logger log.Logger, client *github.Client) *chi.
 	return mux
 }
 
-func boolP(i bool) *bool {
-	return &i
-}
-
-func stringP(i string) *string {
-	return &i
-}
-
-func sliceP(i []string) *[]string {
-	return &i
-}
-
-func contentOrDecode(file string) ([]byte, error) {
-	decoded, err := base64.StdEncoding.DecodeString(
-		file,
-	)
-
-	if err != nil {
-		return os.ReadFile(file)
-	}
-
-	return decoded, nil
-}
-
 func useEnterprise(cfg *config.Config, _ log.Logger) bool {
 	return cfg.Target.BaseURL != ""
 }
@@ -271,7 +246,7 @@ func getClient(cfg *config.Config, logger log.Logger) (*github.Client, error) {
 	}
 
 	if useApplication(cfg, logger) {
-		privateKey, err := contentOrDecode(cfg.Target.PrivateKey)
+		privateKey, err := config.Value(cfg.Target.PrivateKey)
 
 		if err != nil {
 			level.Error(logger).Log(
@@ -286,7 +261,7 @@ func getClient(cfg *config.Config, logger log.Logger) (*github.Client, error) {
 			http.DefaultTransport,
 			cfg.Target.AppID,
 			cfg.Target.InstallID,
-			privateKey,
+			[]byte(privateKey),
 		)
 
 		if err != nil {
@@ -305,12 +280,23 @@ func getClient(cfg *config.Config, logger log.Logger) (*github.Client, error) {
 		), nil
 	}
 
+	accessToken, err := config.Value(cfg.Target.Token)
+
+	if err != nil {
+		level.Error(logger).Log(
+			"msg", "Failed to read token",
+			"err", err,
+		)
+
+		return nil, err
+	}
+
 	return github.NewClient(
 		oauth2.NewClient(
 			context.Background(),
 			oauth2.StaticTokenSource(
 				&oauth2.Token{
-					AccessToken: cfg.Target.Token,
+					AccessToken: accessToken,
 				},
 			),
 		),
@@ -319,7 +305,7 @@ func getClient(cfg *config.Config, logger log.Logger) (*github.Client, error) {
 
 func getEnterprise(cfg *config.Config, logger log.Logger) (*github.Client, error) {
 	if useApplication(cfg, logger) {
-		privateKey, err := contentOrDecode(cfg.Target.PrivateKey)
+		privateKey, err := config.Value(cfg.Target.PrivateKey)
 
 		if err != nil {
 			level.Error(logger).Log(
@@ -334,7 +320,7 @@ func getEnterprise(cfg *config.Config, logger log.Logger) (*github.Client, error
 			http.DefaultTransport,
 			cfg.Target.AppID,
 			cfg.Target.InstallID,
-			privateKey,
+			[]byte(privateKey),
 		)
 
 		if err != nil {
@@ -374,6 +360,17 @@ func getEnterprise(cfg *config.Config, logger log.Logger) (*github.Client, error
 		return client, err
 	}
 
+	accessToken, err := config.Value(cfg.Target.Token)
+
+	if err != nil {
+		level.Error(logger).Log(
+			"msg", "Failed to read token",
+			"err", err,
+		)
+
+		return nil, err
+	}
+
 	client, err := github.NewClient(
 		oauth2.NewClient(
 			context.WithValue(
@@ -389,7 +386,7 @@ func getEnterprise(cfg *config.Config, logger log.Logger) (*github.Client, error
 			),
 			oauth2.StaticTokenSource(
 				&oauth2.Token{
-					AccessToken: cfg.Target.Token,
+					AccessToken: accessToken,
 				},
 			),
 		),

pkg/command/command.go

@@ -112,7 +112,7 @@ func RootFlags(cfg *config.Config) []cli.Flag {
 		&cli.StringFlag{
 			Name:        "github.token",
 			Value:       "",
-			Usage:       "Access token for the GitHub API",
+			Usage:       "Access token for the GitHub API, also supports file:// and base64://",
 			EnvVars:     []string{"GITHUB_EXPORTER_TOKEN"},
 			Destination: &cfg.Target.Token,
 		},
@@ -131,7 +131,7 @@ func RootFlags(cfg *config.Config) []cli.Flag {
 		&cli.StringFlag{
 			Name:        "github.private_key",
 			Value:       "",
-			Usage:       "Private key for the GitHub app, path or base64-encoded",
+			Usage:       "Private key for the GitHub app, also supports file:// and base64://",
 			EnvVars:     []string{"GITHUB_EXPORTER_PRIVATE_KEY"},
 			Destination: &cfg.Target.PrivateKey,
 		},

pkg/config/config.go

@@ -1,6 +1,10 @@
 package config
 
 import (
+	"encoding/base64"
+	"fmt"
+	"os"
+	"strings"
 	"time"
 
 	"github.com/urfave/cli/v2"
@@ -65,3 +69,32 @@ type Config struct {
 func Load() *Config {
 	return &Config{}
 }
+
+// Value returns the config value based on a DSN.
+func Value(val string) (string, error) {
+	if strings.HasPrefix(val, "file://") {
+		content, err := os.ReadFile(
+			strings.TrimPrefix(val, "file://"),
+		)
+
+		if err != nil {
+			return "", fmt.Errorf("failed to parse secret file: %w", err)
+		}
+
+		return string(content), nil
+	}
+
+	if strings.HasPrefix(val, "base64://") {
+		content, err := base64.StdEncoding.DecodeString(
+			strings.TrimPrefix(val, "base64://"),
+		)
+
+		if err != nil {
+			return "", fmt.Errorf("failed to parse base64 value: %w", err)
+		}
+
+		return string(content), nil
+	}
+
+	return val, nil
+}