Add WithDialTLSContextFunc option

config/http_config.go

@@ -414,24 +414,36 @@ func (a *BasicAuth) UnmarshalYAML(unmarshal func(interface{}) error) error {
 // by net.Dialer.
 type DialContextFunc func(context.Context, string, string) (net.Conn, error)
 
+// DialTLSContextFunc defines the signature of the DialContext() function implemented
+// by tls.Dialer.
+type DialTLSContextFunc func(context.Context, string, string) (net.Conn, error)
+
 type httpClientOptions struct {
-	dialContextFunc   DialContextFunc
-	keepAlivesEnabled bool
-	http2Enabled      bool
-	idleConnTimeout   time.Duration
-	userAgent         string
+	dialContextFunc    DialContextFunc
+	dialTLSContextFunc DialTLSContextFunc
+	keepAlivesEnabled  bool
+	http2Enabled       bool
+	idleConnTimeout    time.Duration
+	userAgent          string
 }
 
 // HTTPClientOption defines an option that can be applied to the HTTP client.
 type HTTPClientOption func(options *httpClientOptions)
 
-// WithDialContextFunc allows you to override func gets used for the actual dialing. The default is `net.Dialer.DialContext`.
+// WithDialContextFunc allows you to override the func that gets used for the actual dialing. The default is `net.Dialer.DialContext`.
 func WithDialContextFunc(fn DialContextFunc) HTTPClientOption {
 	return func(opts *httpClientOptions) {
 		opts.dialContextFunc = fn
 	}
 }
 
+// WithDialTLSContextFunc allows you to override the func that gets used for the actual dialing. The default is `tls.Dialer.DialContext`.
+func WithDialTLSContextFunc(fn DialTLSContextFunc) HTTPClientOption {
+	return func(opts *httpClientOptions) {
+		opts.dialTLSContextFunc = fn
+	}
+}
+
 // WithKeepAlivesDisabled allows to disable HTTP keepalive.
 func WithKeepAlivesDisabled() HTTPClientOption {
 	return func(opts *httpClientOptions) {
@@ -519,6 +531,7 @@ func NewRoundTripperFromConfig(cfg HTTPClientConfig, name string, optFuncs ...HT
 			TLSHandshakeTimeout:   10 * time.Second,
 			ExpectContinueTimeout: 1 * time.Second,
 			DialContext:           dialContext,
+			DialTLSContext:        opts.dialTLSContextFunc,
 		}
 		if opts.http2Enabled && cfg.EnableHTTP2 {
 			// HTTP/2 support is golang had many problematic cornercases where

config/http_config_test.go

@@ -545,6 +545,23 @@ func TestCustomDialContextFunc(t *testing.T) {
 	}
 }
 
+func TestCustomDialTLSContextFunc(t *testing.T) {
+	dialFn := func(_ context.Context, _, _ string) (net.Conn, error) {
+		return nil, errors.New(ExpectedError)
+	}
+
+	cfg := HTTPClientConfig{}
+	client, err := NewClientFromConfig(cfg, "test", WithDialTLSContextFunc(dialFn))
+	if err != nil {
+		t.Fatalf("Can't create a client from this config: %+v", cfg)
+	}
+
+	_, err = client.Get("https://localhost")
+	if err == nil || !strings.Contains(err.Error(), ExpectedError) {
+		t.Errorf("Expected error %q but got %q", ExpectedError, err)
+	}
+}
+
 func TestCustomIdleConnTimeout(t *testing.T) {
 	timeout := time.Second * 5
 

model/labels.go

@@ -53,6 +53,10 @@ const (
 	// timeout used to scrape a target.
 	ScrapeTimeoutLabel = "__scrape_timeout__"
 
+	// ServerNameLabel is the name of the label that holds the TLS server name
+	// used to scrape the target.
+	ServerNameLabel = "__server_name__"
+
 	// ReservedLabelPrefix is a prefix which is not legal in user-supplied
 	// label names.
 	ReservedLabelPrefix = "__"