Update default tokenPattern to be more reasonable.

Author: StephenMolloy

samples/SampleWebApp/Web.config

@@ -33,10 +33,12 @@
       <add name="KV4" vaultName="${ConfigBuilderTestKeyVaultName}" mode="Greedy" version="0de51928e49144ce86eb1de9056ac937" type="Microsoft.Configuration.ConfigurationBuilders.AzureKeyVaultConfigBuilder, Microsoft.Configuration.ConfigurationBuilders.Azure, Version=2.0.0.0, Culture=neutral" />
 
       <add name="AS_Sub_Test" optional="${Boolean}" type="Microsoft.Configuration.ConfigurationBuilders.EnvironmentConfigBuilder, Microsoft.Configuration.ConfigurationBuilders.Environment, Version=2.0.0.0, Culture=neutral" />
-  </builders>
+      <add name="AS_Sub_Test2" optional="${app~Settings_Colon-and$friends@super+duper,awesome#cool:Test.}" type="Microsoft.Configuration.ConfigurationBuilders.EnvironmentConfigBuilder, Microsoft.Configuration.ConfigurationBuilders.Environment, Version=2.0.0.0, Culture=neutral" />
+    </builders>
   </configBuilders>
 
   <appSettings configBuilders="Environment,Secrets,Json,KeyPerFile">
+    <add key="app~Settings_Colon-and$friends@super+duper,awesome#cool:Test." value="true" />
     <add key="WINDIR" value="Will be replaced by 'Environment' in Strict and Greedy modes." />
     <add key="SYSTEMDRIVE" value="Will initally be replaced by 'Environment' in Strict and Greedy modes... but then superceded by 'Secrets' in the same modes." />
     <add key="Value_Replaced_By_Environment_In_Expand_Mode" value="${WINDIR}" />
@@ -62,7 +64,7 @@
     <!-- key="Secret3" value="Will be added by KV3:Latest3. IFF already added, will be "updated" by KV1 to Latest3. KV2 and KV4 don't have versions matching this secret." -->
   </appSettings>
 
-  <connectionStrings configBuilders="Json">
+  <connectionStrings configBuilders="Json,AS_Sub_Test2">
     <add name="jsonConnectionString1" connectionString="Will be replaced by 'Json' in 'Flat' AND 'Sectional' jsonModes, but with different values." />
     <add name="connectionStrings:jsonConnectionString1" connectionString="Will only be replaced by 'Json' in 'Flat' jsonMode." />
     <add name="jsonConnectionString2" connectionString="Will only be replaced by 'Json' in 'Sectional' jsonMode." />

src/Base/KeyValueConfigBuilder.cs

@@ -37,30 +37,35 @@ public abstract class KeyValueConfigBuilder : ConfigurationBuilder
         /// Gets or sets the substitution pattern to be used by the KeyValueConfigBuilder.
         /// </summary>
         public KeyValueMode Mode { get; private set; } = KeyValueMode.Strict;
+
         /// <summary>
         /// Gets or sets a prefix string that must be matched by keys to be considered for value substitution.
         /// </summary>
         public string KeyPrefix { get { EnsureInitialized(); return _keyPrefix; } }
         private string _keyPrefix = "";
+
         private bool StripPrefix { get { EnsureInitialized(); return _stripPrefix; } }
         private bool _stripPrefix = false;  // Prefix-stripping is all handled in this base class; this is private so it doesn't confuse sub-classes.
         /// <summary>
         /// Specifies whether the config builder should cause errors if the backing source cannot be found.
         /// </summary>
         public bool Optional { get { EnsureInitialized(); return _optional; } protected set { _optional = value; } }
         private bool _optional = true;
+
         /// <summary>
         /// Gets or sets a regular expression used for matching tokens in raw xml during Greedy substitution.
         /// </summary>
         public string TokenPattern { get { EnsureInitialized(); return _tokenPattern; } protected set { _tokenPattern = value; } }
-        private string _tokenPattern = @"\$\{(\w+)\}";
+        //private string _tokenPattern = @"\$\{(\w+)\}";
+        private string _tokenPattern = @"\$\{(\w[\w-_$@#+,.:~]*)\}";    // Updated to be more reasonable for V2
 
         /// <summary>
         /// Looks up a single 'value' for the given 'key.'
         /// </summary>
         /// <param name="key">The 'key' to look up in the config source. (Prefix handling is not needed here.)</param>
         /// <returns>The value corresponding to the given 'key' or null if no value is found.</returns>
         public abstract string GetValue(string key);
+
         /// <summary>
         /// Retrieves all known key/value pairs for the configuration source where the key begins with with <paramref name="prefix"/>.
         /// </summary>
@@ -74,6 +79,7 @@ public abstract class KeyValueConfigBuilder : ConfigurationBuilder
         /// <param name="key">The string to be validated. May be partial.</param>
         /// <returns>True if the string is valid. False if the string is not a valid key.</returns>
         public virtual bool ValidateKey(string key) { return true; }
+
         /// <summary>
         /// Transforms the raw key to a new string just before updating items in Strict and Greedy modes.
         /// </summary>