S3: Format x-amz-date with year-of-era (#679)

"YYYY" in `DateTimeFormatter.ofPattern("YYYYMMdd")` means
week-based-year, which formats `LocalDate.of(2017, 12, 31)` as
"20181231" and results in unexpected rejections from S3 as below:

> The difference between the request time and the current time is
too large.

Replacing it with "yyyy" fixes the bug.

s3/src/main/scala/akka/stream/alpakka/s3/auth/Signer.scala

@@ -15,7 +15,7 @@ import com.amazonaws.auth
 import com.amazonaws.auth._
 
 private[alpakka] object Signer {
-  private val dateFormatter = DateTimeFormatter.ofPattern("YYYYMMdd'T'HHmmssX")
+  private val dateFormatter = DateTimeFormatter.ofPattern("yyyyMMdd'T'HHmmssX")
 
   def signedRequest(request: HttpRequest, key: SigningKey, date: ZonedDateTime = ZonedDateTime.now(ZoneOffset.UTC))(
       implicit mat: Materializer

s3/src/test/scala/akka/stream/alpakka/s3/auth/SignerSpec.scala

@@ -4,7 +4,8 @@
 
 package akka.stream.alpakka.s3.auth
 
-import java.time.{LocalDate, LocalDateTime, ZoneOffset}
+import java.time.{LocalDate, LocalDateTime, ZoneOffset, ZonedDateTime}
+
 import akka.actor.ActorSystem
 import akka.http.scaladsl.model.{HttpMethods, HttpRequest}
 import akka.http.scaladsl.model.headers.{Host, RawHeader}
@@ -26,8 +27,9 @@ class SignerSpec(_system: ActorSystem) extends TestKit(_system) with FlatSpecLik
   val credentials = new AWSStaticCredentialsProvider(
     new BasicAWSCredentials("AKIDEXAMPLE", "wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY")
   )
-  val scope = CredentialScope(LocalDate.of(2015, 8, 30), "us-east-1", "iam")
-  val signingKey = SigningKey(credentials, scope)
+
+  def scope(date: LocalDate) = CredentialScope(date, "us-east-1", "iam")
+  def signingKey(dateTime: ZonedDateTime) = SigningKey(credentials, scope(dateTime.toLocalDate))
 
   val cr = CanonicalRequest(
     "GET",
@@ -40,7 +42,7 @@ class SignerSpec(_system: ActorSystem) extends TestKit(_system) with FlatSpecLik
 
   "Signer" should "calculate the string to sign" in {
     val date = LocalDateTime.of(2015, 8, 30, 12, 36, 0).atZone(ZoneOffset.UTC)
-    val stringToSign: String = Signer.stringToSign("AWS4-HMAC-SHA256", signingKey, date, cr)
+    val stringToSign: String = Signer.stringToSign("AWS4-HMAC-SHA256", signingKey(date), date, cr)
     stringToSign should equal(
       "AWS4-HMAC-SHA256\n20150830T123600Z\n20150830/us-east-1/iam/aws4_request\nf536975d06c0309214f805bb90ccff089219ecd68b2577efef23edd43b7e1a59"
     )
@@ -54,8 +56,9 @@ class SignerSpec(_system: ActorSystem) extends TestKit(_system) with FlatSpecLik
         RawHeader("Content-Type", "application/x-www-form-urlencoded; charset=utf-8")
       )
 
+    val date = LocalDateTime.of(2015, 8, 30, 12, 36, 0).atZone(ZoneOffset.UTC)
     val srFuture =
-      Signer.signedRequest(req, signingKey, LocalDateTime.of(2015, 8, 30, 12, 36, 0).atZone(ZoneOffset.UTC))
+      Signer.signedRequest(req, signingKey(date), date)
     whenReady(srFuture) { signedRequest =>
       signedRequest should equal(
         HttpRequest(HttpMethods.GET)
@@ -74,4 +77,16 @@ class SignerSpec(_system: ActorSystem) extends TestKit(_system) with FlatSpecLik
     }
   }
 
+  it should "format x-amz-date based on year-of-era instead of week-based-year" in {
+    val req = HttpRequest(HttpMethods.GET)
+      .withUri("https://iam.amazonaws.com/?Action=ListUsers&Version=2010-05-08")
+
+    val date = LocalDateTime.of(2017, 12, 31, 12, 36, 0).atZone(ZoneOffset.UTC)
+    val srFuture =
+      Signer.signedRequest(req, signingKey(date), date)
+
+    whenReady(srFuture) { signedRequest =>
+      signedRequest.getHeader("x-amz-date").get.value should equal("20171231T123600Z")
+    }
+  }
 }