Updated constant and usage details

Author: rahulnirgude

clients/src/main/java/org/apache/kafka/common/config/SslConfigs.java

@@ -90,8 +90,8 @@ public class SslConfigs {
         + "This is optional for client and can be used for two-way authentication for client.";
 
     public static final String SSL_KEYSTORE_ALIAS_CONFIG = "ssl.keystore.alias";
-    public static final String SSL_KEYSTORE_ALIAS_DOC = "The Alias of key in the key store file. "
-            + "This is optional for client and can be used for two-way authentication for client.";
+    public static final String SSL_KEYSTORE_ALIAS_DOC = "This is config is used to pick named alias from the keystore to build the SSL engine and authenticate the client with broker. " +
+            "This is an optional config and used only when you have multiple keys in the keystore and you need to control which key needs to be presented to server.";
 
 
     public static final String SSL_KEYSTORE_PASSWORD_CONFIG = "ssl.keystore.password";

clients/src/main/java/org/apache/kafka/common/security/ssl/DefaultSslEngineFactory.java

@@ -286,7 +286,7 @@ private SSLContext createSSLContext(SecurityStore keystore, SecurityStore trusts
             String tmfAlgorithm = this.tmfAlgorithm != null ? this.tmfAlgorithm : TrustManagerFactory.getDefaultAlgorithm();
             TrustManager[] trustManagers = getTrustManagers(truststore, tmfAlgorithm);
 
-            sslContext.init(applyAliasToKM(keyManagers, (String)configs.get("ssl.keystore.alias")), trustManagers, this.secureRandomImplementation);
+            sslContext.init(applyAliasToKM(keyManagers, (String)configs.get(SslConfigs.SSL_KEYSTORE_ALIAS_CONFIG)), trustManagers, this.secureRandomImplementation);
             log.debug("Created SSL context with keystore {}, truststore {}, provider {}.",
                     keystore, truststore, sslContext.getProvider().getName());
             return sslContext;