Helper class to sign and populate Authorization header akka#3253

1. Populates required date and version header
2. Reads current request and create authorization token as per AWS requirements
3. Populates authorization header

azure-storage/src/main/scala/akka/stream/alpakka/azure/storage/impl/auth/Signer.scala

@@ -0,0 +1,102 @@
+/*
+ * Copyright (C) since 2016 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package akka.stream.alpakka
+package azure
+package storage
+package impl.auth
+
+import akka.NotUsed
+import akka.http.scaladsl.model.{HttpRequest, Uri}
+import akka.http.scaladsl.model.headers._
+import akka.stream.scaladsl.Source
+
+import java.util.Base64
+import javax.crypto.Mac
+import javax.crypto.spec.SecretKeySpec
+
+/** Takes initial request and add signed `Authorization` header and essential XMS headers.
+ *
+ * @param initialRequest
+ *   - Initial HTTP request without authorization and XMS headers
+ * @param settings
+ *   - Storage settings
+ */
+final case class Signer(initialRequest: HttpRequest, settings: StorageSettings) {
+
+  private val credential = settings.azureNameKeyCredential
+  private val requestWithHeaders =
+    initialRequest
+      .addHeader(RawHeader(XmsDateHeaderKey, getFormattedDate))
+      .addHeader(RawHeader(XmsVersionHeaderKey, settings.apiVersion))
+
+  private val mac = {
+    val mac = Mac.getInstance(settings.algorithm)
+    mac.init(new SecretKeySpec(credential.accountKey, settings.algorithm))
+    mac
+  }
+
+  def signedRequest: Source[HttpRequest, NotUsed] =
+    if (settings.authorizationType == "anon") Source.single(requestWithHeaders)
+    else {
+      val contentLengthValue = getHeaderValue(`Content-Length`.name, "0")
+      val contentLength = if (contentLengthValue == "0") "" else contentLengthValue
+
+      val headersToSign = Seq(
+          requestWithHeaders.method.value.toUpperCase,
+          getHeaderValue(`Content-Encoding`.name, ""),
+          getHeaderValue("Content-Language", ""),
+          contentLength,
+          getHeaderValue("Content-MD5", ""),
+          getHeaderValue(`Content-Type`.name, ""),
+          "", // date, we are using `x-ms-date` instead
+          getHeaderValue(`If-Modified-Since`.name, ""),
+          getHeaderValue(`If-Match`.name, ""),
+          getHeaderValue(`If-None-Match`.name, ""),
+          getHeaderValue(`If-Unmodified-Since`.name, ""),
+          getHeaderValue(Range.name, "")
+        ) ++ getAdditionalXmsHeaders ++ getCanonicalizedResource
+
+      val signature = sign(headersToSign)
+
+      Source.single(
+        requestWithHeaders.addHeader(
+          RawHeader(AuthorizationHeaderKey, s"${settings.authorizationType} ${credential.accountName}:$signature")
+        )
+      )
+    }
+
+  private def getHeaderOptionalValue(headerName: String) =
+    requestWithHeaders.headers.collectFirst {
+      case header if header.name() == headerName => header.value()
+    }
+
+  private def getHeaderValue(headerName: String, defaultValue: String) =
+    getHeaderOptionalValue(headerName).getOrElse(defaultValue)
+
+  private def getAdditionalXmsHeaders =
+    requestWithHeaders.headers.filter(header => header.name().startsWith("x-ms-")).sortBy(_.name()).map { header =>
+      s"${header.name()}:${header.value()}"
+    }
+
+  private def getCanonicalizedResource = {
+    val uri = requestWithHeaders.uri
+    val resourcePath = s"/${credential.accountName}${uri.path.toString()}"
+
+    val queries =
+      uri.queryString() match {
+        case Some(queryString) =>
+          Uri.Query(queryString).toMap.toSeq.sortBy(_._1).map {
+            case (key, value) => s"$key:$value"
+          }
+
+        case None => Seq.empty[String]
+      }
+
+    Seq(resourcePath) ++ queries
+  }
+
+  private def sign(headersToSign: Seq[String]) =
+    Base64.getEncoder.encodeToString(mac.doFinal(headersToSign.mkString(NewLine).getBytes))
+}