[EXPORTER] Allow custom HttpClient in OTLP HTTP

CHANGELOG.md

@@ -51,6 +51,9 @@ Increment the:
 * [CODE HEALTH] Fix clang-tidy performance enum size warnings
   [#3923](https://github.com/open-telemetry/opentelemetry-cpp/pull/3923)
 
+* [EXPORTER] Allow custom HttpClient in OTLP HTTP
+  [#3930](https://github.com/open-telemetry/opentelemetry-cpp/pull/3930)
+
 Important changes:
 
 * [BUILD] Revisit EventLogger deprecation

exporters/otlp/include/opentelemetry/exporters/otlp/otlp_http_client.h

@@ -158,6 +158,14 @@ class OtlpHttpClient
    */
   explicit OtlpHttpClient(OtlpHttpClientOptions &&options);
 
+  /**
+   * Create an OtlpHttpClient using the specified http client.
+   * @param options the Otlp http client options to be used for exporting
+   * @param http_client the http client to be used for exporting
+   */
+  OtlpHttpClient(OtlpHttpClientOptions &&options,
+                 std::shared_ptr<ext::http::client::HttpClient> http_client);
+
   ~OtlpHttpClient();
   OtlpHttpClient(const OtlpHttpClient &)            = delete;
   OtlpHttpClient &operator=(const OtlpHttpClient &) = delete;
@@ -266,20 +274,6 @@ class OtlpHttpClient
    */
   bool cleanupGCSessions() noexcept;
 
-  // For testing
-  friend class OtlpHttpExporterTestPeer;
-  friend class OtlpHttpLogRecordExporterTestPeer;
-  friend class OtlpHttpMetricExporterTestPeer;
-
-  /**
-   * Create an OtlpHttpClient using the specified http client.
-   * Only tests can call this constructor directly.
-   * @param options the Otlp http client options to be used for exporting
-   * @param http_client the http client to be used for exporting
-   */
-  OtlpHttpClient(OtlpHttpClientOptions &&options,
-                 std::shared_ptr<ext::http::client::HttpClient> http_client);
-
   // Stores if this HTTP client had its Shutdown() method called
   std::atomic<bool> is_shutdown_;