fix: don't sign Expect header in SigV4

.changes/d4ba7f85-24f3-4925-8bb4-25020f294b9a.json

@@ -0,0 +1,8 @@
+{
+    "id": "d4ba7f85-24f3-4925-8bb4-25020f294b9a",
+    "type": "bugfix",
+    "description": "Skip signing the `Expect` header in SigV4",
+    "issues": [
+        "awslabs/aws-sdk-kotlin#862"
+    ]
+}

runtime/auth/aws-signing-default/common/src/aws/smithy/kotlin/runtime/auth/awssigning/Canonicalizer.kt

@@ -59,9 +59,10 @@ internal interface Canonicalizer {
     ): CanonicalRequest
 }
 
-// Taken from https://github.com/awslabs/aws-c-auth/blob/31d573c0dd328db5775f7a55650d27b8c08311ba/source/aws_signing.c#L118-L151
+// Taken from https://github.com/awslabs/aws-c-auth/blob/dd505b55fd46222834f35c6e54165d8cbebbfaaa/source/aws_signing.c#L118-L156
 private val skipHeaders = setOf(
     "connection",
+    "expect", // https://github.com/awslabs/aws-sdk-kotlin/issues/862
     "sec-websocket-key",
     "sec-websocket-protocol",
     "sec-websocket-version",

runtime/auth/aws-signing-default/common/test/aws/smithy/kotlin/runtime/auth/awssigning/DefaultCanonicalizerTest.kt

@@ -97,4 +97,37 @@ class DefaultCanonicalizerTest {
 
         assertEquals("/2013-04-01/healthcheck/foo%253Cbar%253Ebaz%253C%252Fbar%253E", uri.canonicalPath(config))
     }
+
+    @Test
+    fun testUnsignedHeaders() = runTest {
+        val request = HttpRequest {
+            method = HttpMethod.GET
+            url { host = Host.Domain("bar.amazonaws.com") }
+            headers {
+                // These should be signed
+                set("Content-Type", "application/x-www-form-urlencoded; charset=utf-8")
+                set("x-amz-user-agent", "baz")
+
+                // These should not be signed
+                set("Expect", "100-continue")
+                set("X-Amzn-Trace-Id", "qux")
+            }
+            body = HttpBody.Empty
+        }
+
+        val signingDateString = "20150830T123600Z"
+        val config = AwsSigningConfig {
+            region = "foo"
+            service = "bar"
+            signingDate = Instant.fromIso8601(signingDateString)
+            credentialsProvider = testCredentialsProvider
+        }
+        val credentials = Credentials("foo", "bar") // anything without a session token set
+
+        val canonicalizer = Canonicalizer.Default
+        val actual = canonicalizer.canonicalRequest(request, config, credentials)
+
+        val expectedSignedHeaders = "content-type;host;x-amz-date;x-amz-user-agent"
+        assertEquals(expectedSignedHeaders, actual.signedHeaders)
+    }
 }