```kotlin
    dependencies {
       // define a BOM and its version
       implementation(platform("com.squareup.okhttp3:okhttp-bom:4.12.0"))

       // define any required OkHttp artifacts without version
       implementation("com.squareup.okhttp3:okhttp")
       implementation("com.squareup.okhttp3:logging-interceptor")

 * return null; // Didn't find a preemptive auth scheme.
 * ```
 *
 * ## Reactive Authentication
 *
 * Implementations authenticate by returning a follow-up request that includes an authorization
 * header, or they may decline the challenge by returning null. In this case the unauthenticated
 * response will be returned to the caller that triggered it.
 *
 * Implementations should check if the initial request already included an attempt to

 *
 * Each entry is 4 bytes, and represents a _range_ of code points that all share a common 14-bit
 * prefix. Entries are sorted by their complete code points.
 *
 * The 4 bytes are named b0, b1, b2 and b3. We also define these supplemental values:
 *
 *  * **b2a**: b2 + 0x80
 *  * **b3a**: b3 + 0x80
 *  * **b2b3**: (b2 << 7) + b3
 *
 * b0
 * --
 *

  constructor(name: ByteString, value: String) : this(name, value.encodeUtf8())

  override fun toString(): String = "${name.utf8()}: ${value.utf8()}"

  companion object {
    // Special header names defined in HTTP/2 spec.
    @JvmField val PSEUDO_PREFIX: ByteString = ":".encodeUtf8()

    const val RESPONSE_STATUS_UTF8 = ":status"
    const val TARGET_METHOD_UTF8 = ":method"
    const val TARGET_PATH_UTF8 = ":path"

   */
  @Throws(IOException::class)
  fun execute(): Response

  /**
   * Schedules the request to be executed at some point in the future.
   *
   * The [dispatcher][OkHttpClient.dispatcher] defines when the request will run: usually
   * immediately unless there are several other requests currently being executed.
   *
   * This client will later call back `responseCallback` with either an HTTP response or a failure

 * that is currently executing does not impact the ongoing run, but it does prevent a recurrence
 * from being scheduled.
 *
 * Tasks may opt-out of cancellation with `cancelable = false`. Such tasks will recur until they
 * decide not to by returning -1L.
 *
 * Task Queues
 * -----------
 *
 * Tasks are bound to the [TaskQueue] they are scheduled in. Each queue is sequential and the tasks

### Application Interceptors

Interceptors are registered as either _application_ or _network_ interceptors. We'll use the `LoggingInterceptor` defined above to show the difference.

Register an _application_ interceptor by calling `addInterceptor()` on `OkHttpClient.Builder`:

```java
OkHttpClient client = new OkHttpClient.Builder()
    .addInterceptor(new LoggingInterceptor())
    .build();

Request request = new Request.Builder()

    assertThat(statusLine.message).isEqualTo("")
    assertThat(statusLine.protocol).isEqualTo(Protocol.HTTP_1_1)
    assertThat(statusLine.code).isEqualTo(code)
  }

  /**
   * This is not defined in the protocol but some servers won't add the leading empty space when the
   * message is empty. http://www.w3.org/Protocols/rfc2616/rfc2616-sec6.html#sec6.1
   */
  @Test
  fun emptyMessageAndNoLeadingSpace() {

   * designed for this nonstandard interaction will use it. As of 2019-01, the only widely-used
   * implementation of this pattern is [gRPC][grpc].
   *
   * Because the encoding of interleaved data is not well-defined for HTTP/1, duplex request
   * bodies may only be used with HTTP/2. Calls to HTTP/1 servers will fail before the HTTP request
   * is transmitted. If you cannot ensure that your client and server both support HTTP/2, do not

    .addSubjectAlternativeName("localhost")
    .build();
```

[`HandshakeCertificates`][handshake_certificates] keeps the certificates for a TLS handshake.
Use its [builder][handshake_certificates_builder] to define which certificates the HTTPS server
returns to its clients. The returned instance can create an `SSLSocketFactory` that implements this
policy:

```java