Adding more tests to show how a string marked with the jsonvalue trait and encoded as a base64 header should be decoded

Author: cenedhryn

core/protocols/aws-json-protocol/src/main/java/software/amazon/awssdk/protocols/json/internal/unmarshall/HeaderUnmarshaller.java

@@ -43,6 +43,9 @@ private HeaderUnmarshaller() {
 
     /**
      * Unmarshalls a string header, taking into account whether it's a Base 64 encoded JSON value.
+     * <p>
+     * <em>Note:</em> This code does no attempt to validate whether the unmarshalled string does, in fact, represent valid
+     * JSON values. The string value is returned as-is, and it's up to the user to validate the results.
      *
      * @param value Value to unmarshall
      * @param field {@link SdkField} containing metadata about member being unmarshalled.

test/protocol-tests-core/src/main/resources/software/amazon/awssdk/protocol/suites/cases/rest-json-output.json

@@ -38,7 +38,7 @@
     }
   },
   {
-    "description": "Base 64 string header with JSON trait is decoded",
+    "description": "Base 64 string header with JSON trait is decoded, unquoted string preserved (invalid json)",
     "given": {
       "response": {
         "status_code": 200,
@@ -59,6 +59,50 @@
       }
     }
   },
+  {
+    "description": "Base 64 string header with JSON trait is decoded, quoted string preserved (valid json)",
+    "given": {
+      "response": {
+        "status_code": 200,
+        "headers": {
+          "Encoded-Header": "InRvRGVjb2RlIg=="
+        },
+        "body": "{\"JsonValueMember\":\"dontDecode\"}"
+      }
+    },
+    "when": {
+      "action": "unmarshall",
+      "operation": "JsonValuesOperation"
+    },
+    "then": {
+      "deserializedAs": {
+        "JsonValueHeaderMember": "\"toDecode\"",
+        "JsonValueMember": "dontDecode"
+      }
+    }
+  },
+  {
+    "description": "Base 64 string header with JSON trait is decoded, quoted json object preserved",
+    "given": {
+      "response": {
+        "status_code": 200,
+        "headers": {
+          "Encoded-Header": "IntcImxpc3RcIjpbMSwyLDNdLFwibWFwXCI6e1wiZmlyc3RcIjpcInZhbHVlMVwiLFwic2Vjb25kXCI6XCJ2YWx1ZTJcIn19Ig=="
+        },
+        "body": "{\"JsonValueMember\":\"dontDecode\"}"
+      }
+    },
+    "when": {
+      "action": "unmarshall",
+      "operation": "JsonValuesOperation"
+    },
+    "then": {
+      "deserializedAs": {
+        "JsonValueHeaderMember": "\"{\\\"list\\\":[1,2,3],\\\"map\\\":{\\\"first\\\":\\\"value1\\\",\\\"second\\\":\\\"value2\\\"}}\"",
+        "JsonValueMember": "dontDecode"
+      }
+    }
+  },
   {
     "description": "ISO 8601 Timestamp in header unmarshalled correctly",
     "given": {