Update reference docs for access to HTTP headers

Also rename existing methods for request headers to be consistent with
those for response headers and use "Http" in the name.

Closes gh-74

spring-graphql-docs/src/docs/asciidoc/testing.adoc

@@ -88,6 +88,30 @@ For tests against a live, running server:
 	WebGraphQlTester tester = WebGraphQlTester.builder(client).build();
 ----
 
+`WebGraphQlTester` supports setting HTTP request headers and access to HTTP response
+headers. This may be useful to inspect or set security related headers.
+
+[source,java,indent=0,subs="verbatim,quotes"]
+----
+	this.graphQlTester.queryName("{ myQuery }")
+			.httpHeaders(headers -> headers.setBasicAuth("rob", "..."))
+			.execute()
+			.httpHeadersSatisfy(headers -> {
+				// check response headers
+			})
+			.path("myQuery.field1").entity(String.class).isEqualTo("value1")
+			.path("myQuery.field2").entity(String.class).isEqualTo("value2");
+----
+
+You can also set default request headers at the builder level:
+
+[source,java,indent=0,subs="verbatim,quotes"]
+----
+	WebGraphQlTester tester = WebGraphQlTester.builder(client)
+		.defaultHttpHeaders(headers -> headers.setBasicAuth("rob", "..."))
+		.build();
+----
+
 
 
 [[testing-queries]]