[8.19](backport #47712) [libbeat] aws auth method: fix service name and region overwrite

x-pack/libbeat/common/aws/signer.go

@@ -81,8 +81,8 @@ func initializeSignerTransport(logger *logp.Logger, defaultServiceName string, d
 			})
 		}),
 		logger:      logger,
-		serviceName: defaultRegion,
-		region:      defaultServiceName,
+		serviceName: defaultServiceName,
+		region:      defaultRegion,
 		now:         time.Now,
 	}
 }

x-pack/libbeat/common/aws/signer_test.go

@@ -73,6 +73,26 @@
 			},
 			expectedRequestBody: []byte{},
 		},
+		{
+			name:               "no body overwrite service name and region",
+			defaultServiceName: "guardduty",
+			defaultRegion:      "us-east-1",
+			url:                "https://guardduty2.us-east-2.amazonaws.com/detector/abc123/findings",
+			requestBody:        http.NoBody,
+			requestHeaders:     map[string]string{},
+			credentials:        fakeStaticCreds,
+			now:                now,
+			initMockRoundTripper: func(mrt *mockRoundTripper) {
+				mrt.On("RoundTrip", mock.Anything).Return(&http.Response{}, nil).Once()
+			},
+			expectError: false,
+			expectedRequestHeaders: map[string]string{
+				"Authorization":        "AWS4-HMAC-SHA256 Credential=AKIAIOSFODNN7EXAMPLE/20251011/us-east-1/guardduty/aws4_request, SignedHeaders=host;x-amz-date;x-amz-security-token, Signature=2bc3ea894efa9703ec95cac0bdcd6a1067a64636058b66e88640af2dc06ff2dd",
+				"X-Amz-Date":           "20251011T160000Z",
+				"X-Amz-Security-Token": "session",
+			},
+			expectedRequestBody: []byte{},
+		},
 		{
 			name:               "with body",
 			defaultServiceName: "",
@@ -128,6 +148,9 @@
 			st := initializeSignerTransport(logger, tc.defaultServiceName, tc.defaultRegion, tc.credentials, &m)
 			st.now = tc.now
 
+			assert.Equal(t, tc.defaultServiceName, st.serviceName)
+			assert.Equal(t, tc.defaultRegion, st.region)
+
 			req, err := http.NewRequestWithContext(t.Context(), http.MethodGet, tc.url, tc.requestBody)
 			require.NoError(t, err)
 			for k, v := range tc.requestHeaders {
@@ -145,7 +168,7 @@
 			for k := range m.req.Header {
 				gotHeaders[k] = m.req.Header.Get(k)
 			}
 			assert.EqualValues(t, tc.expectedRequestHeaders, gotHeaders)
 
 			// ensure that request's body is readable (and not consumed) after the hash operation.
 			b, err := io.ReadAll(req.Body)