diff --git a/client/client.go b/client/client.go
index 02b6a2e..8681870 100644
--- a/client/client.go
+++ b/client/client.go
@@ -97,29 +97,30 @@ var DefaultErrorHandler = func(res *http.Response, uri string) error {
 
 // TimeoutOption is an option to set timeout for the http client calls
 // value unit is nanoseconds
-//
-// Deprecated: Internal http.Client shouldn't be modified after construction. Use WithHttpClient instead
 func TimeoutOption(timeout time.Duration) Option {
 	return func(request *Request) error {
-		request.SetTimeout(timeout)
+		httpClient, ok := request.HttpClient.(*http.Client)
+		if !ok {
+			return errors.New("unable to set timeout: httpclient is not *http.Client")
+		}
 
+		httpClient.Timeout = timeout
 		return nil
 	}
 }
 
-// Deprecated: Internal http.Client shouldn't be modified after construction. Use WithHttpClient instead
 func ProxyOption(proxyURL string) Option {
 	return func(request *Request) error {
 		if proxyURL == "" {
 			return nil
 		}
 
-		err := request.SetProxy(proxyURL)
-		if err != nil {
-			return err
+		httpClient, ok := request.HttpClient.(*http.Client)
+		if !ok {
+			return errors.New("unable to set proxy: httpclient is not *http.Client")
 		}
 
-		return nil
+		return setHttpClientTransportProxy(httpClient, proxyURL)
 	}
 }
 
@@ -130,6 +131,13 @@ func WithHttpClient(httpClient HTTPClient) Option {
 	}
 }
 
+func WithExtraHeader(key, value string) Option {
+	return func(request *Request) error {
+		request.Headers[key] = value
+		return nil
+	}
+}
+
 func WithExtraHeaders(headers map[string]string) Option {
 	return func(request *Request) error {
 		for k, v := range headers {
@@ -169,3 +177,25 @@ func (r *Request) SetProxy(proxyUrl string) error {
 func (r *Request) AddHeader(key, value string) {
 	r.Headers[key] = value
 }
+
+func setHttpClientTransportProxy(client *http.Client, proxyUrl string) error {
+	if proxyUrl == "" {
+		return errors.New("empty proxy url")
+	}
+	url, err := url.Parse(proxyUrl)
+	if err != nil {
+		return err
+	}
+
+	if client.Transport == nil {
+		client.Transport = &http.Transport{Proxy: http.ProxyURL(url)}
+		return nil
+	}
+
+	transport, ok := client.Transport.(*http.Transport)
+	if !ok {
+		return errors.New("http client transport is not *http.Transport")
+	}
+	transport.Proxy = http.ProxyURL(url)
+	return nil
+}
diff --git a/client/client_test.go b/client/client_test.go
index d4d7892..5be62b7 100644
--- a/client/client_test.go
+++ b/client/client_test.go
@@ -12,6 +12,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestRequest_GetBase(t *testing.T) {
@@ -199,3 +200,71 @@ func (c *mockJSONClient) Do(_ *http.Request) (*http.Response, error) {
 		Body:       io.NopCloser(bytes.NewBuffer(c.body)),
 	}, nil
 }
+
+func TestInitClientOptions(t *testing.T) {
+	const aBaseURL = "http://www.example.com/"
+	tests := []struct {
+		name      string
+		options   []Option
+		assertion func(t *testing.T, client *Request)
+	}{
+		{
+			name:    "set proxy",
+			options: []Option{ProxyOption("http://www.example.com")},
+			assertion: func(t *testing.T, client *Request) {
+				// checks that the proxy is set
+				url, err := client.HttpClient.(*http.Client).Transport.(*http.Transport).Proxy(&http.Request{})
+				require.NoError(t, err)
+				require.Equal(t, "http://www.example.com", url.String())
+			},
+		},
+		{
+			name:    "set timeout",
+			options: []Option{TimeoutOption(3 * time.Second)},
+			assertion: func(t *testing.T, client *Request) {
+				// checks that the timeout is set
+				require.Equal(t, 3*time.Second, client.HttpClient.(*http.Client).Timeout)
+			},
+		},
+		{
+			name:    "set proxy&timeout",
+			options: []Option{ProxyOption("http://www.example.com"), TimeoutOption(3 * time.Second)},
+			assertion: func(t *testing.T, client *Request) {
+				// checks that the proxy is set
+				url, err := client.HttpClient.(*http.Client).Transport.(*http.Transport).Proxy(&http.Request{})
+				require.NoError(t, err)
+				require.Equal(t, "http://www.example.com", url.String())
+
+				// checks that the timeout is set
+				require.Equal(t, 3*time.Second, client.HttpClient.(*http.Client).Timeout)
+			},
+		},
+		{
+			name: "WithExtraHeader multiple times",
+			options: []Option{
+				WithExtraHeader("Content-Type", "application/json"),
+				WithExtraHeader("Accept", "application/json"),
+				WithExtraHeader("Server", "Apache"),
+				WithExtraHeaders(map[string]string{
+					"Authorization": "Basic <credentials>",
+					"Connection":    "Keep-Alive",
+					"Server":        "nginx",
+				}),
+			},
+			assertion: func(t *testing.T, client *Request) {
+				require.Equal(t, "application/json", client.Headers["Content-Type"])
+				require.Equal(t, "application/json", client.Headers["Accept"])
+				require.Equal(t, "Basic <credentials>", client.Headers["Authorization"])
+				require.Equal(t, "Keep-Alive", client.Headers["Connection"])
+				require.Equal(t, "nginx", client.Headers["Server"])
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			c := InitClient(aBaseURL, nil, test.options...)
+			test.assertion(t, &c)
+		})
+	}
+}