Enable setting config via cmd line args

Author: DamianEdwards

src/Benchmarks/ConfigurationConfigurationProvider.cs

@@ -0,0 +1,57 @@
+// Copyright (c) .NET Foundation. All rights reserved. 
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information. 
+
+using System;
+
+namespace Microsoft.Extensions.Configuration
+{
+    public static class ConfigurationExtensions
+    {
+        public static IConfigurationBuilder AddConfiguration(this IConfigurationBuilder builder, IConfiguration source)
+        {
+            return builder.Add(new ConfigurationConfigurationProvider(source));
+        }
+
+        public static IConfigurationBuilder AddConfiguration(this IConfigurationBuilder builder, string prefix, IConfiguration source)
+        {
+            return builder.Add(new ConfigurationConfigurationProvider(prefix, source));
+        }
+    }
+
+    public class ConfigurationConfigurationProvider : ConfigurationProvider
+    {
+        public ConfigurationConfigurationProvider(IConfiguration source)
+            : this(null, source)
+        {
+
+        }
+
+        public ConfigurationConfigurationProvider(string prefix, IConfiguration source)
+        {
+            if (source == null)
+            {
+                throw new ArgumentNullException(nameof(source));
+            }
+
+            if (prefix == null)
+            {
+                foreach (var pair in source.GetChildren())
+                {
+                    Data.Add(pair.Key, pair.Value);
+                }
+            }
+            else
+            {
+                var pairs = source.GetChildren();
+
+                foreach (var pair in pairs)
+                {
+                    if (pair.Key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
+                    {
+                        Data.Add(pair.Key.Substring(prefix.Length), pair.Value);
+                    }
+                }
+            }
+        }
+    }
+}

src/Benchmarks/Startup.cs

@@ -24,6 +24,12 @@ public Startup(IHostingEnvironment env)
                 .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                 .AddEnvironmentVariables();
 
+            if (env.Configuration != null)
+            {
+                // This allows passing of config values via the cmd line, e.g.: dnx web --app.EnableDbTests=true
+                builder.AddConfiguration("app.", env.Configuration);
+            }
+
             Configuration = builder.Build();
 
             Configuration.Bind(StartupOptions);