KAFKA-6562: Make jackson-databind an optional clients dependency (#5110)

Use `provided` scope in Maven.

Reviewers: Rajini Sivaram <rajinisivaram@googlemail.com>, Ismael Juma <ismael@juma.me.uk>

build.gradle

@@ -785,11 +785,20 @@ project(':examples') {
 project(':clients') {
   archivesBaseName = "kafka-clients"
 
+  configurations {
+    jacksonDatabindConfig
+  }
+
+  // add jacksonDatabindConfig as provided scope config with high priority (1000)
+  conf2ScopeMappings.addMapping(1000, configurations.jacksonDatabindConfig, "provided")
+
   dependencies {
     compile libs.lz4
     compile libs.snappy
     compile libs.slf4jApi
-    compile libs.jacksonDatabind // for SASL/OAUTHBEARER bearer token parsing
+    compileOnly libs.jacksonDatabind // for SASL/OAUTHBEARER bearer token parsing
+
+    jacksonDatabindConfig libs.jacksonDatabind // to publish as provided scope dependency.
 
     testCompile libs.bcpkix
     testCompile libs.junit
@@ -798,6 +807,7 @@ project(':clients') {
     testCompile libs.powermockEasymock
 
     testRuntime libs.slf4jlog4j
+    testRuntime libs.jacksonDatabind
   }
 
   task determineCommitId {

docs/security.html

@@ -715,6 +715,8 @@
                 <pre>
     security.protocol=SASL_SSL (or SASL_PLAINTEXT if non-production)
     sasl.mechanism=OAUTHBEARER</pre></li>
+             <li>The default implementation of SASL/OAUTHBEARER depends on the jackson-databind library.
+                 Since it's an optional dependency, users have to configure it as a dependency via their build tool.</li>
             </ol>
         </li>
         <li><h5><a id="security_sasl_oauthbearer_unsecured_retrieval" href="#security_sasl_oauthbearer_unsecured_retrieval">Unsecured Token Creation Options for SASL/OAUTHBEARER</a></h5>