Creating a webservice that accepts XML as a string - asp.net

Question

I have been trying to create a webservice that needs to allow the client to send thru 3 parameters being Username, Password and XML_In all 3 of type string. This then sends the variables to a Stored procedure which processes the data and returns an XML string which is then returned to the client.
The Stored procedure works 100% but I'm getting an error with the XML being sent thru as a string. From reading up most gave the suggestion of adding <httpRuntime requestValidationMode="2.0"/> and <pages validateRequest="false"> to my web.config which works but that would then apply to my entire site which I dont want at all.
The other suggestion was to place it in the #Page part but that does not apply to a web service as it has no user defined layout. Please see my code below and help. I'm still quite a newbie to .Net thus the reason I'm doing 90% of it in SQL.
The error That gets returned is :
System.Web.HttpRequestValidationException: A potentially dangerous Request.Form value was detected from the client (XML_In="<senddata><settings ...").
at System.Web.HttpRequest.ValidateString(String value, String collectionKey, RequestValidationSource requestCollection)
at System.Web.HttpRequest.ValidateHttpValueCollection(HttpValueCollection collection, RequestValidationSource requestCollection)
at System.Web.HttpRequest.get_Form()
at System.Web.Services.Protocols.HtmlFormParameterReader.Read(HttpRequest request)
at System.Web.Services.Protocols.HttpServerProtocol.ReadParameters()
at System.Web.Services.Protocols.WebServiceHandler.CoreProcessRequest()
here's the code:
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.ComponentModel
Imports System.Xml
Imports JumpStart.Framework.Database
' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
' <System.Web.Script.Services.ScriptService()> _
<System.Web.Services.WebService(Namespace:="http://mydomainname.co.za/")> _
<System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
Public Class LeadProcessor
Inherits System.Web.Services.WebService
<WebMethod()> _
Public Function Lead_Processing(ByVal UserName As String, ByVal PassWord As String, ByVal XML_In As String) As XmlDocument
Dim poDSL As New DSL
Dim Result As String
Dim XML_Out = New XmlDocument()
Result = poDSL.ExecuteProcedure_ExecuteScalar("DECLARE #Result XML " & _
"EXEC [dbo].[APP_InsertLeadFromXML] " & _
"#Username = N'" & UserName & "', " & _
"#Password = N'" & PassWord & "', " & _
"#ParmListXML = '" & XML_In.ToString & "', " & _
"#XMLResult = #Result OUTPUT " & _
"SELECT #Result")
XML_Out.LoadXml(Result)
Return XML_Out
End Function

Answer 1

I agree with CodeCaster comment (new projects - WCF or WebApi).
But if you can't change it now, consider use a XMLDocument as parameter, or an XElemento, or directly, do a Base64 transform of the text, in order to avoid that errors.
Code for your service' client:
your_proxy.Lead_Processing(sUserName, sPassWord, Convert.ToBase64String(Encoding.UTF8.GetBytes(sXML))
Then, in your service, do this
<WebMethod()> _
Public Function Lead_Processing(ByVal UserName As String, ByVal PassWord As String, ByVal XML_In As String) As XmlDocument
Dim oData As Byte() = Convert.FromBase64String(XML_In)
Dim sDecodedXML As String = System.Text.Encoding.UTF8.GetString(oData)
Dim poDSL As New DSL
Dim Result As String
Dim XML_Out = New XmlDocument()
Result = poDSL.ExecuteProcedure_ExecuteScalar("DECLARE #Result XML " & _
"EXEC [dbo].[APP_InsertLeadFromXML] " & _
"#Username = N'" & UserName & "', " & _
"#Password = N'" & PassWord & "', " & _
"#ParmListXML = '" & sDecodedXML & "', " & _
"#XMLResult = #Result OUTPUT " & _
"SELECT #Result")
XML_Out.LoadXml(Result)
Return XML_Out
End Function
Hope it helps
Edit:
Your service with base64.
We're telling that Asmx it's almost a legacy tech. New projects may use WCF tech (I can't teach you WCF in a few lines).
You can put that code into your asmx service. You can use that code in the way I edited my answer.