Closes #85.

src/Cadru.Scim/FilterExpression.cs

@@ -44,7 +44,13 @@ public class FilterExpression : IFilterExpression
         /// <inheritdoc/>
         public string ToFilterExpression(bool prependQuerySeprator = true)
         {
-            return $@"{(prependQuerySeprator ? "?" : "")}filter={ this }";
+            return this.ToFilterExpression(new FilterExpressionFormatOptions { IncludeQuerySeparator = prependQuerySeprator });
+        }
+
+        /// <inheritdoc/>
+        public string ToFilterExpression(FilterExpressionFormatOptions options)
+        {
+            return $@"{(options.IncludeQuerySeparator ? "?" : "")}{(options.IncludeFilterParameterName ? "filter=" : "")}{ this }";
         }
 
         /// <summary>

src/Cadru.Scim/FilterExpressionFormatOptions.cs

@@ -0,0 +1,42 @@
+//------------------------------------------------------------------------------
+// <copyright file="IFilter.cs"
+//  company="Scott Dorman"
+//  library="Cadru">
+//    Copyright (C) 2001-2020 Scott Dorman.
+// </copyright>
+//
+// <license>
+//    Licensed under the Microsoft Public License (Ms-PL) (the "License");
+//    you may not use this file except in compliance with the License.
+//    You may obtain a copy of the License at
+//
+//    http://opensource.org/licenses/Ms-PL.html
+//
+//    Unless required by applicable law or agreed to in writing, software
+//    distributed under the License is distributed on an "AS IS" BASIS,
+//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//    See the License for the specific language governing permissions and
+//    limitations under the License.
+// </license>
+//------------------------------------------------------------------------------
+
+namespace Cadru.Scim.Filters
+{
+    /// <summary>
+    /// Provides options to be used when formatting an <see cref="IFilter"/>.
+    /// </summary>
+    public sealed class FilterExpressionFormatOptions
+    {
+        /// <summary>
+        /// To prepend the "?" query string separator,
+        /// <see langword="true"/>; otherwise, <see langword="false"/>
+        /// </summary>
+        public bool IncludeQuerySeparator { get; set; } = true;
+
+        /// <summary>
+        /// To prepend the "filter=" query string parameter key,
+        /// <see langword="true"/>; otherwise, <see langword="false"/>
+        /// </summary>
+        public bool IncludeFilterParameterName { get; set; } = true;
+    }
+}

src/Cadru.Scim/FilterGroup.cs

@@ -42,7 +42,13 @@ public class FilterGroup : IFilterGroup
         /// <inheritdoc/>
         public string ToFilterExpression(bool prependQuerySeprator = true)
         {
-            return $"?filter={ this }";
+            return this.ToFilterExpression(new FilterExpressionFormatOptions { IncludeQuerySeparator = prependQuerySeprator });
+        }
+
+        /// <inheritdoc/>
+        public string ToFilterExpression(FilterExpressionFormatOptions options)
+        {
+            return $@"{(options.IncludeQuerySeparator ? "?" : "")}{(options.IncludeFilterParameterName ? "filter=" : "")}{ this }";
         }
 
         /// <summary>
@@ -52,23 +58,12 @@ public string ToFilterExpression(bool prependQuerySeprator = true)
         /// <returns>A string that represents the current <see cref="FilterGroup"></see>.</returns>
         public override string ToString()
         {
-            var brackets = Array.Empty<string>();
-            switch (this.GroupingCharacter)
+            var brackets = this.GroupingCharacter switch
             {
-                case GroupingCharacter.Parentheses:
-                    brackets = new string[]
-                    {
-                        "(", ")"
-                    };
-                    break;
-
-                case GroupingCharacter.SquareBracket:
-                    brackets = new string[]
-                    {
-                        "[", "]"
-                    };
-                    break;
-            }
+                GroupingCharacter.Parentheses => new string[] { "(", ")" },
+                GroupingCharacter.SquareBracket => new string[] { "[", "]" },
+                _ => new string[] { String.Empty, String.Empty }
+            };
 
             return $"{ brackets[0] }{ String.Join($" { this.LogicalOperator } ", this.Filters) }{ brackets[1] }";
         }

src/Cadru.Scim/IFilter.cs

@@ -29,13 +29,23 @@ public interface IFilter
     {
         /// <summary>
         /// Returns a string that represents the current
-        /// <see cref="FilterExpression"></see> as a valid query
+        /// <see cref="IFilter"></see> as a valid query
         /// </summary>
         /// <param name="prependQuerySeprator">
         /// To prepend the "?" query string separator,
         /// <see langword="true"></see>; otherwise, <see langword="false"></see>.
         /// </param>
-        /// <returns>A string that represents the current <see cref="FilterExpression"></see>.</returns>
+        /// <returns>A string that represents the current <see cref="IFilter"/>.</returns>
         string ToFilterExpression(bool prependQuerySeprator = true);
+
+        /// <summary>
+        /// Returns a string that represents the current
+        /// <see cref="IFilter"></see> as a valid query
+        /// </summary>
+        /// <param name="options">
+        /// The options to use when formatting the <see cref="IFilter"/>.
+        /// </param>
+        /// <returns>A string that represents the current <see cref="IFilter"/>.</returns>
+        string ToFilterExpression(FilterExpressionFormatOptions options);
     }
 }

src/Cadru.Scim/NotFilterGroup.cs

@@ -43,7 +43,13 @@ public class NotFilterGroup : IFilterGroup
         /// <inheritdoc/>
         public string ToFilterExpression(bool prependQuerySeprator = true)
         {
-            return $"?filter={ this }";
+            return this.ToFilterExpression(new FilterExpressionFormatOptions { IncludeQuerySeparator = prependQuerySeprator });
+        }
+
+        /// <inheritdoc/>
+        public string ToFilterExpression(FilterExpressionFormatOptions options)
+        {
+            return $@"{(options.IncludeQuerySeparator ? "?" : "")}{(options.IncludeFilterParameterName ? "filter=" : "")}{ this }";
         }
 
         /// <summary>