Add KeyCredentialTrait (Azure#36540)

Author: srnagar

sdk/core/azure-core/CHANGELOG.md

@@ -3,6 +3,7 @@
 ## 1.43.0-beta.1 (Unreleased)
 
 ### Features Added
+- Added `KeyCredentialTrait` interface. Client builders that implement this interface will support key-based authentication.
 
 ### Breaking Changes
 

sdk/core/azure-core/src/main/java/com/azure/core/client/traits/KeyCredentialTrait.java

@@ -0,0 +1,30 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.core.client.traits;
+
+import com.azure.core.credential.KeyCredential;
+
+/**
+ * An {@link com.azure.core.client.traits Azure SDK for Java trait} providing a consistent interface for setting
+ * {@link KeyCredential}. Refer to the Azure SDK for Java
+ * <a href="https://aka.ms/azsdk/java/docs/identity">identity and authentication</a>
+ * documentation for more details on proper usage of the {@link KeyCredential} type.
+ *
+ * @param <T> The concrete type that implements the trait. This is required so that fluent operations can continue
+ * to return the concrete type, rather than the trait type.
+ * @see com.azure.core.client.traits
+ * @see KeyCredential
+ */
+public interface KeyCredentialTrait<T> {
+    /**
+     * Sets the {@link KeyCredential} used for authentication. Refer to the Azure SDK for Java
+     * <a href="https://aka.ms/azsdk/java/docs/identity">identity and authentication</a>
+     * documentation for more details on proper usage of the {@link KeyCredential} type.
+     *
+     * @param credential the {@link KeyCredential} to be used for authentication.
+     * @return Returns the same concrete type with the appropriate properties updated, to allow for fluent chaining of
+     *      operations.
+     */
+    T credential(KeyCredential credential);
+}