Adds function to securely read header values from our requests

lib/web/Get-IcingaRESTHeaderValue.psm1

@@ -0,0 +1,17 @@
+function Get-IcingaRESTHeaderValue()
+{
+    param(
+        [hashtable]$Request = @{},
+        [string]$Header     = $null
+    );
+
+    if ($null -eq $Request -or [string]::IsNullOrEmpty($Header) -Or $Request.Count -eq 0) {
+        return $null;
+    }
+
+    if ($Request.Header.ContainsKey($Header) -eq $FALSE) {
+        return $null
+    }
+
+    return $Request.Header[$Header];
+}