diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache
index 18f64464c8e..c5d0f13b5e1 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache
@@ -7,18 +7,18 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
     {{#jvm-retrofit2}}
-    ext.retrofitVersion = '2.7.2'
+    ext.retrofitVersion = '2.9.0'
     {{/jvm-retrofit2}}
     {{#useRxJava}}
     ext.rxJavaVersion = '1.3.8'
     {{/useRxJava}}
     {{#useRxJava2}}
-    ext.rxJava2Version = '2.2.20'
+    ext.rxJava2Version = '2.2.21'
     {{/useRxJava2}}
     {{#useRxJava3}}
-    ext.rxJava3Version = '3.0.10'
+    ext.rxJava3Version = '3.0.12'
     {{/useRxJava3}}
 
     repositories {
@@ -52,67 +52,67 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
     {{#moshi}}
     {{^moshiCodeGen}}
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
     {{/moshiCodeGen}}
     {{#moshiCodeGen}}
-    compile "com.squareup.moshi:moshi:1.11.0"
-    kapt "com.squareup.moshi:moshi-kotlin-codegen:1.11.0"
+    implementation "com.squareup.moshi:moshi:1.12.0"
+    kapt "com.squareup.moshi:moshi-kotlin-codegen:1.12.0"
     {{/moshiCodeGen}}
     {{/moshi}}
     {{#gson}}
-    compile "com.google.code.gson:gson:2.8.6"
+    implementation "com.google.code.gson:gson:2.8.7"
     {{/gson}}
     {{#jackson}}
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.fasterxml.jackson.module:jackson-module-kotlin:2.12.1"
-    compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.12.1"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.fasterxml.jackson.module:jackson-module-kotlin:2.12.3"
+    implementation "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.12.3"
     {{/jackson}}
     {{#kotlinx_serialization}}
-    compile "org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.1"
+    implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.1"
     {{/kotlinx_serialization}}
     {{#jvm-okhttp3}}
-    compile "com.squareup.okhttp3:okhttp:3.12.13"
+    implementation "com.squareup.okhttp3:okhttp:3.12.13"
     {{/jvm-okhttp3}}
     {{#jvm-okhttp4}}
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
     {{/jvm-okhttp4}}
     {{#threetenbp}}
-    compile "org.threeten:threetenbp:1.5.0"
+    implementation "org.threeten:threetenbp:1.5.1"
     {{/threetenbp}}
     {{#jvm-retrofit2}}
     {{#hasOAuthMethods}}
-    compile "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.0"
+    implementation "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.2"
     {{/hasOAuthMethods}}
-    compile "com.squareup.okhttp3:logging-interceptor:4.9.0"
+    implementation "com.squareup.okhttp3:logging-interceptor:4.9.1"
     {{#useRxJava}}
-    compile "io.reactivex:rxjava:$rxJavaVersion"
-    compile "com.squareup.retrofit2:adapter-rxjava:$retrofitVersion"
+    implementation "io.reactivex:rxjava:$rxJavaVersion"
+    implementation "com.squareup.retrofit2:adapter-rxjava:$retrofitVersion"
     {{/useRxJava}}
     {{#useRxJava2}}
-    compile "io.reactivex.rxjava2:rxjava:$rxJava2Version"
-    compile "com.squareup.retrofit2:adapter-rxjava2:$retrofitVersion"
+    implementation "io.reactivex.rxjava2:rxjava:$rxJava2Version"
+    implementation "com.squareup.retrofit2:adapter-rxjava2:$retrofitVersion"
     {{/useRxJava2}}
     {{#useRxJava3}}
-    compile "io.reactivex.rxjava3:rxjava:$rxJava3Version"
-    compile "com.squareup.retrofit2:adapter-rxjava3:2.9.0"
+    implementation "io.reactivex.rxjava3:rxjava:$rxJava3Version"
+    implementation "com.squareup.retrofit2:adapter-rxjava3:2.9.0"
     {{/useRxJava3}}
-    compile "com.squareup.retrofit2:retrofit:$retrofitVersion"
+    implementation "com.squareup.retrofit2:retrofit:$retrofitVersion"
     {{#gson}}
-    compile "com.squareup.retrofit2:converter-gson:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-gson:$retrofitVersion"
     {{/gson}}
     {{#moshi}}
-    compile "com.squareup.retrofit2:converter-moshi:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-moshi:$retrofitVersion"
     {{/moshi}}
     {{#kotlinx_serialization}}
-    compile "com.jakewharton.retrofit:retrofit2-kotlinx-serialization-converter:0.8.0"
+    implementation "com.jakewharton.retrofit:retrofit2-kotlinx-serialization-converter:0.8.0"
     {{/kotlinx_serialization}}
-    compile "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
     {{/jvm-retrofit2}}
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
 {{#kotlinx_serialization}}
 
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/auth/OAuthOkHttpClient.kt.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/auth/OAuthOkHttpClient.kt.mustache
index 106b0581994..5c30002e94b 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/auth/OAuthOkHttpClient.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/auth/OAuthOkHttpClient.kt.mustache
@@ -13,14 +13,13 @@ import okhttp3.OkHttpClient
 import okhttp3.Request
 import okhttp3.MediaType.Companion.toMediaTypeOrNull
 import okhttp3.RequestBody
+import okhttp3.RequestBody.Companion.toRequestBody
 
 
 class OAuthOkHttpClient(
-        private var client: OkHttpClient
+        private var client: OkHttpClient = OkHttpClient()
 ) : HttpClient {
 
-    constructor() : this(OkHttpClient())
-
     @Throws(OAuthSystemException::class, OAuthProblemException::class)
     override fun <T : OAuthClientResponse?> execute(
             request: OAuthClientRequest, 
@@ -39,7 +38,7 @@ class OAuthOkHttpClient(
             }
         }
 
-        val body: RequestBody? = if (request.body != null) RequestBody.create(mediaType, request.body) else null
+        val body: RequestBody? = if (request.body != null) request.body.toRequestBody(mediaType) else null
         requestBuilder.method(requestMethod, body)
 
         try {
@@ -48,6 +47,7 @@ class OAuthOkHttpClient(
                     response.body?.string(), 
                     response.body?.contentType()?.toString(),
                     response.code,
+                    response.headers.toMultimap(),
                     responseClass)
         } catch (e: IOException) {
             throw OAuthSystemException(e)
diff --git a/samples/client/petstore/kotlin-gson/build.gradle b/samples/client/petstore/kotlin-gson/build.gradle
index a99b1cf2af2..5cad8581cb6 100644
--- a/samples/client/petstore/kotlin-gson/build.gradle
+++ b/samples/client/petstore/kotlin-gson/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,8 +28,8 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "com.google.code.gson:gson:2.8.6"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "com.google.code.gson:gson:2.8.7"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-jackson/build.gradle b/samples/client/petstore/kotlin-jackson/build.gradle
index 0429e1f7c30..5cbe1fb014f 100644
--- a/samples/client/petstore/kotlin-jackson/build.gradle
+++ b/samples/client/petstore/kotlin-jackson/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,10 +28,10 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.fasterxml.jackson.module:jackson-module-kotlin:2.12.1"
-    compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.12.1"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.fasterxml.jackson.module:jackson-module-kotlin:2.12.3"
+    implementation "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.12.3"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-json-request-string/build.gradle b/samples/client/petstore/kotlin-json-request-string/build.gradle
index 378951fb75a..189e54f8195 100644
--- a/samples/client/petstore/kotlin-json-request-string/build.gradle
+++ b/samples/client/petstore/kotlin-json-request-string/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -29,9 +29,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-jvm-okhttp4-coroutines/build.gradle b/samples/client/petstore/kotlin-jvm-okhttp4-coroutines/build.gradle
index a99b1cf2af2..5cad8581cb6 100644
--- a/samples/client/petstore/kotlin-jvm-okhttp4-coroutines/build.gradle
+++ b/samples/client/petstore/kotlin-jvm-okhttp4-coroutines/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,8 +28,8 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "com.google.code.gson:gson:2.8.6"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "com.google.code.gson:gson:2.8.7"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-moshi-codegen/build.gradle b/samples/client/petstore/kotlin-moshi-codegen/build.gradle
index 7fec302dc5a..ff73803f4b6 100644
--- a/samples/client/petstore/kotlin-moshi-codegen/build.gradle
+++ b/samples/client/petstore/kotlin-moshi-codegen/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -29,9 +29,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "com.squareup.moshi:moshi:1.11.0"
-    kapt "com.squareup.moshi:moshi-kotlin-codegen:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "com.squareup.moshi:moshi:1.12.0"
+    kapt "com.squareup.moshi:moshi-kotlin-codegen:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-nonpublic/build.gradle b/samples/client/petstore/kotlin-nonpublic/build.gradle
index 260bd6bda6e..bb575e6e4bf 100644
--- a/samples/client/petstore/kotlin-nonpublic/build.gradle
+++ b/samples/client/petstore/kotlin-nonpublic/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,9 +28,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-nullable/build.gradle b/samples/client/petstore/kotlin-nullable/build.gradle
index 260bd6bda6e..bb575e6e4bf 100644
--- a/samples/client/petstore/kotlin-nullable/build.gradle
+++ b/samples/client/petstore/kotlin-nullable/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,9 +28,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-okhttp3/build.gradle b/samples/client/petstore/kotlin-okhttp3/build.gradle
index e872269b3fb..4d9f2f630d4 100644
--- a/samples/client/petstore/kotlin-okhttp3/build.gradle
+++ b/samples/client/petstore/kotlin-okhttp3/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,9 +28,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:3.12.13"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:3.12.13"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/build.gradle b/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/build.gradle
index f7a6d02171e..60257e31601 100644
--- a/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/build.gradle
+++ b/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/build.gradle
@@ -7,8 +7,8 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
-    ext.retrofitVersion = '2.7.2'
+    ext.kotlin_version = '1.5.10'
+    ext.retrofitVersion = '2.9.0'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -31,14 +31,14 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.1"
-    compile "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.0"
-    compile "com.squareup.okhttp3:logging-interceptor:4.9.0"
-    compile "com.squareup.retrofit2:retrofit:$retrofitVersion"
-    compile "com.jakewharton.retrofit:retrofit2-kotlinx-serialization-converter:0.8.0"
-    compile "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.1"
+    implementation "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.2"
+    implementation "com.squareup.okhttp3:logging-interceptor:4.9.1"
+    implementation "com.squareup.retrofit2:retrofit:$retrofitVersion"
+    implementation "com.jakewharton.retrofit:retrofit2-kotlinx-serialization-converter:0.8.0"
+    implementation "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
 
 tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
diff --git a/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt b/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
index 93adbda3fc9..aa70ca9d2f1 100644
--- a/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
+++ b/samples/client/petstore/kotlin-retrofit2-kotlinx_serialization/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
@@ -13,14 +13,13 @@ import okhttp3.OkHttpClient
 import okhttp3.Request
 import okhttp3.MediaType.Companion.toMediaTypeOrNull
 import okhttp3.RequestBody
+import okhttp3.RequestBody.Companion.toRequestBody
 
 
 class OAuthOkHttpClient(
-        private var client: OkHttpClient
+        private var client: OkHttpClient = OkHttpClient()
 ) : HttpClient {
 
-    constructor() : this(OkHttpClient())
-
     @Throws(OAuthSystemException::class, OAuthProblemException::class)
     override fun <T : OAuthClientResponse?> execute(
             request: OAuthClientRequest, 
@@ -39,7 +38,7 @@ class OAuthOkHttpClient(
             }
         }
 
-        val body: RequestBody? = if (request.body != null) RequestBody.create(mediaType, request.body) else null
+        val body: RequestBody? = if (request.body != null) request.body.toRequestBody(mediaType) else null
         requestBuilder.method(requestMethod, body)
 
         try {
@@ -48,6 +47,7 @@ class OAuthOkHttpClient(
                     response.body?.string(), 
                     response.body?.contentType()?.toString(),
                     response.code,
+                    response.headers.toMultimap(),
                     responseClass)
         } catch (e: IOException) {
             throw OAuthSystemException(e)
diff --git a/samples/client/petstore/kotlin-retrofit2-rx3/build.gradle b/samples/client/petstore/kotlin-retrofit2-rx3/build.gradle
index 3ddd8d97e8f..2f5e94a4fcd 100644
--- a/samples/client/petstore/kotlin-retrofit2-rx3/build.gradle
+++ b/samples/client/petstore/kotlin-retrofit2-rx3/build.gradle
@@ -7,9 +7,9 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
-    ext.retrofitVersion = '2.7.2'
-    ext.rxJava3Version = '3.0.10'
+    ext.kotlin_version = '1.5.10'
+    ext.retrofitVersion = '2.9.0'
+    ext.rxJava3Version = '3.0.12'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -30,15 +30,15 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.0"
-    compile "com.squareup.okhttp3:logging-interceptor:4.9.0"
-    compile "io.reactivex.rxjava3:rxjava:$rxJava3Version"
-    compile "com.squareup.retrofit2:adapter-rxjava3:2.9.0"
-    compile "com.squareup.retrofit2:retrofit:$retrofitVersion"
-    compile "com.squareup.retrofit2:converter-moshi:$retrofitVersion"
-    compile "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.2"
+    implementation "com.squareup.okhttp3:logging-interceptor:4.9.1"
+    implementation "io.reactivex.rxjava3:rxjava:$rxJava3Version"
+    implementation "com.squareup.retrofit2:adapter-rxjava3:2.9.0"
+    implementation "com.squareup.retrofit2:retrofit:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-moshi:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-retrofit2-rx3/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt b/samples/client/petstore/kotlin-retrofit2-rx3/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
index 93adbda3fc9..aa70ca9d2f1 100644
--- a/samples/client/petstore/kotlin-retrofit2-rx3/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
+++ b/samples/client/petstore/kotlin-retrofit2-rx3/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
@@ -13,14 +13,13 @@ import okhttp3.OkHttpClient
 import okhttp3.Request
 import okhttp3.MediaType.Companion.toMediaTypeOrNull
 import okhttp3.RequestBody
+import okhttp3.RequestBody.Companion.toRequestBody
 
 
 class OAuthOkHttpClient(
-        private var client: OkHttpClient
+        private var client: OkHttpClient = OkHttpClient()
 ) : HttpClient {
 
-    constructor() : this(OkHttpClient())
-
     @Throws(OAuthSystemException::class, OAuthProblemException::class)
     override fun <T : OAuthClientResponse?> execute(
             request: OAuthClientRequest, 
@@ -39,7 +38,7 @@ class OAuthOkHttpClient(
             }
         }
 
-        val body: RequestBody? = if (request.body != null) RequestBody.create(mediaType, request.body) else null
+        val body: RequestBody? = if (request.body != null) request.body.toRequestBody(mediaType) else null
         requestBuilder.method(requestMethod, body)
 
         try {
@@ -48,6 +47,7 @@ class OAuthOkHttpClient(
                     response.body?.string(), 
                     response.body?.contentType()?.toString(),
                     response.code,
+                    response.headers.toMultimap(),
                     responseClass)
         } catch (e: IOException) {
             throw OAuthSystemException(e)
diff --git a/samples/client/petstore/kotlin-retrofit2/build.gradle b/samples/client/petstore/kotlin-retrofit2/build.gradle
index 6674970e550..ec9a8e9ac24 100644
--- a/samples/client/petstore/kotlin-retrofit2/build.gradle
+++ b/samples/client/petstore/kotlin-retrofit2/build.gradle
@@ -7,8 +7,8 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
-    ext.retrofitVersion = '2.7.2'
+    ext.kotlin_version = '1.5.10'
+    ext.retrofitVersion = '2.9.0'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -29,13 +29,13 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.0"
-    compile "com.squareup.okhttp3:logging-interceptor:4.9.0"
-    compile "com.squareup.retrofit2:retrofit:$retrofitVersion"
-    compile "com.squareup.retrofit2:converter-moshi:$retrofitVersion"
-    compile "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.2"
+    implementation "com.squareup.okhttp3:logging-interceptor:4.9.1"
+    implementation "com.squareup.retrofit2:retrofit:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-moshi:$retrofitVersion"
+    implementation "com.squareup.retrofit2:converter-scalars:$retrofitVersion"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-retrofit2/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt b/samples/client/petstore/kotlin-retrofit2/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
index 93adbda3fc9..aa70ca9d2f1 100644
--- a/samples/client/petstore/kotlin-retrofit2/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
+++ b/samples/client/petstore/kotlin-retrofit2/src/main/kotlin/org/openapitools/client/auth/OAuthOkHttpClient.kt
@@ -13,14 +13,13 @@ import okhttp3.OkHttpClient
 import okhttp3.Request
 import okhttp3.MediaType.Companion.toMediaTypeOrNull
 import okhttp3.RequestBody
+import okhttp3.RequestBody.Companion.toRequestBody
 
 
 class OAuthOkHttpClient(
-        private var client: OkHttpClient
+        private var client: OkHttpClient = OkHttpClient()
 ) : HttpClient {
 
-    constructor() : this(OkHttpClient())
-
     @Throws(OAuthSystemException::class, OAuthProblemException::class)
     override fun <T : OAuthClientResponse?> execute(
             request: OAuthClientRequest, 
@@ -39,7 +38,7 @@ class OAuthOkHttpClient(
             }
         }
 
-        val body: RequestBody? = if (request.body != null) RequestBody.create(mediaType, request.body) else null
+        val body: RequestBody? = if (request.body != null) request.body.toRequestBody(mediaType) else null
         requestBuilder.method(requestMethod, body)
 
         try {
@@ -48,6 +47,7 @@ class OAuthOkHttpClient(
                     response.body?.string(), 
                     response.body?.contentType()?.toString(),
                     response.code,
+                    response.headers.toMultimap(),
                     responseClass)
         } catch (e: IOException) {
             throw OAuthSystemException(e)
diff --git a/samples/client/petstore/kotlin-string/build.gradle b/samples/client/petstore/kotlin-string/build.gradle
index 260bd6bda6e..bb575e6e4bf 100644
--- a/samples/client/petstore/kotlin-string/build.gradle
+++ b/samples/client/petstore/kotlin-string/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,9 +28,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-threetenbp/build.gradle b/samples/client/petstore/kotlin-threetenbp/build.gradle
index 1d988072386..b4e0d0acc7a 100644
--- a/samples/client/petstore/kotlin-threetenbp/build.gradle
+++ b/samples/client/petstore/kotlin-threetenbp/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,10 +28,10 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    compile "org.threeten:threetenbp:1.5.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    implementation "org.threeten:threetenbp:1.5.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin-uppercase-enum/build.gradle b/samples/client/petstore/kotlin-uppercase-enum/build.gradle
index 260bd6bda6e..bb575e6e4bf 100644
--- a/samples/client/petstore/kotlin-uppercase-enum/build.gradle
+++ b/samples/client/petstore/kotlin-uppercase-enum/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,9 +28,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }
diff --git a/samples/client/petstore/kotlin/build.gradle b/samples/client/petstore/kotlin/build.gradle
index 260bd6bda6e..bb575e6e4bf 100644
--- a/samples/client/petstore/kotlin/build.gradle
+++ b/samples/client/petstore/kotlin/build.gradle
@@ -7,7 +7,7 @@ wrapper {
 }
 
 buildscript {
-    ext.kotlin_version = '1.5.0'
+    ext.kotlin_version = '1.5.10'
 
     repositories {
         maven { url "https://repo1.maven.org/maven2" }
@@ -28,9 +28,9 @@ test {
 }
 
 dependencies {
-    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
-    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
-    compile "com.squareup.moshi:moshi-kotlin:1.11.0"
-    compile "com.squareup.okhttp3:okhttp:4.9.0"
-    testCompile "io.kotlintest:kotlintest-runner-junit5:3.4.2"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
+    implementation "com.squareup.moshi:moshi-kotlin:1.12.0"
+    implementation "com.squareup.okhttp3:okhttp:4.9.1"
+    testImplementation "io.kotlintest:kotlintest-runner-junit5:3.4.2"
 }