Add URL substitution enum value validation

Author: calebkiage

Diff for: src/Microsoft.OpenApi/Extensions/OpenApiServerExtensions.cs

@@ -17,7 +17,9 @@ public static class OpenApiServerExtensions
     /// <param name="values">The server variable values that will be used to replace the default values.</param>
     /// <returns>A URL with the provided variables substituted.</returns>
     /// <exception cref="ArgumentException">
-    /// If a substitution has no value in the supplied dictionary or the default
+    /// Thrown when:
+    ///   1. A substitution has no valid value in both the supplied dictionary and the default
+    ///   2. A substitution's value is not available in the enum provided
     /// </exception>
     public static string ReplaceServerUrlVariables(this OpenApiServer server, IDictionary<string, string> values)
     {
@@ -35,6 +37,12 @@ public static string ReplaceServerUrlVariables(this OpenApiServer server, IDicti
                 throw new ArgumentException(
                     string.Format(SRResource.ParseServerUrlDefaultValueNotAvailable, variable.Key), nameof(server));
             }
+
+            if (variable.Value.Enum?.Contains(actualValue) != true)
+            {
+                throw new ArgumentException(
+                    string.Format(SRResource.ParseServerUrlValueNotValid, actualValue, variable.Key), nameof(values));
+            }
             parsedUrl = parsedUrl.Replace($"{{{variable.Key}}}", actualValue);
         }
         return parsedUrl;

Diff for: src/Microsoft.OpenApi/Properties/SRResource.Designer.cs

@@ -228,4 +228,7 @@
   <data name="ParseServerUrlDefaultValueNotAvailable" xml:space="preserve">
       <value>Invalid server variable '{0}'. A value was not provided and no default value was provided.</value>
   </data>
+  <data name="ParseServerUrlValueNotValid" xml:space="preserve">
+      <value>Value '{0}' is not a valid value for variable '{1}'.</value>
+  </data>
 </root>

Diff for: src/Microsoft.OpenApi/Properties/SRResource.resx

@@ -79,7 +79,7 @@ public void ShouldFailIfProvidedValueIsNotInEnum()
 
         Assert.Throws<ArgumentException>(() =>
         {
-            variable.ReplaceServerUrlVariables(new Dictionary<string, string> {{"version", "v2"}});
+            variable.ReplaceServerUrlVariables(new Dictionary<string, string> {{"version", "v3"}});
         });
     }
 }