pkg/oauth2: dependency-inject grants total counter metric

cmd/telemeter-server/main.go

@@ -23,6 +23,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
+
 	oidc "github.com/coreos/go-oidc"
 	"github.com/oklog/run"
 	"github.com/spf13/cobra"
@@ -250,8 +252,17 @@ func (o *Options) Run() error {
 				Endpoint: provider.Endpoint(),
 			}
 
+			grantsTotal := prometheus.NewCounter(
+				prometheus.CounterOpts{
+					Name: "telemeter_password_credentials_grants_total",
+					Help: "Tracks the number of resource owner password credential grants.",
+				},
+			)
+
+			prometheus.MustRegister(grantsTotal)
+
 			src := telemeter_oauth2.NewPasswordCredentialsTokenSource(
-				ctx, &cfg,
+				ctx, &cfg, grantsTotal.Inc,
 				o.AuthorizeUsername, o.AuthorizePassword,
 			)
 

pkg/oauth2/token_source.go

@@ -7,27 +7,14 @@ import (
 	"sync"
 	"time"
 
-	"github.com/prometheus/client_golang/prometheus"
 	"golang.org/x/oauth2"
 )
 
-var (
-	grantsTotal = prometheus.NewCounter(
-		prometheus.CounterOpts{
-			Name: "password_credentials_grants_total",
-			Help: "Tracks the number of resource owner password credential grants.",
-		},
-	)
-)
-
-func init() {
-	prometheus.MustRegister(grantsTotal)
-}
-
 type passwordCredentialsTokenSource struct {
 	ctx                context.Context
 	cfg                *oauth2.Config
 	username, password string
+	grantsCounter      func()
 
 	mu                sync.Mutex // protects the fields below
 	refreshToken      *oauth2.Token
@@ -47,12 +34,13 @@ type passwordCredentialsTokenSource struct {
 // using the given resource owner and password.
 //
 // It is safe for concurrent use.
-func NewPasswordCredentialsTokenSource(ctx context.Context, cfg *oauth2.Config, username, password string) *passwordCredentialsTokenSource {
+func NewPasswordCredentialsTokenSource(ctx context.Context, cfg *oauth2.Config, grantsCounter func(), username, password string) *passwordCredentialsTokenSource {
 	return &passwordCredentialsTokenSource{
-		ctx:      ctx,
-		username: username,
-		password: password,
-		cfg:      cfg,
+		ctx:           ctx,
+		username:      username,
+		password:      password,
+		cfg:           cfg,
+		grantsCounter: grantsCounter,
 	}
 }
 
@@ -95,7 +83,7 @@ func (c *passwordCredentialsTokenSource) Token() (*oauth2.Token, error) {
 }
 
 func (c *passwordCredentialsTokenSource) passwordCredentialsToken() (*oauth2.Token, error) {
-	grantsTotal.Inc()
+	c.grantsCounter()
 
 	tok, err := c.cfg.PasswordCredentialsToken(c.ctx, c.username, c.password)
 	if err != nil {

pkg/oauth2/token_source_test.go

@@ -80,7 +80,8 @@ func TestPasswordCredentialsTokenSource(t *testing.T) {
 				},
 			)
 
-			src := NewPasswordCredentialsTokenSource(ctx, conf, username, password)
+			nop := func() {}
+			src := NewPasswordCredentialsTokenSource(ctx, conf, nop, username, password)
 			return src, tr
 		}
 	}