Async login against either the Partner or Enterprise SOAP API

Login.cs

static async Task<T> Login<T>(string userName, string password, string orgId)
{
    string url;
    string soap;
    string wsdlType;

    if (typeof(T) == typeof(Enterprise.LoginResult))
    {
        url = "https://login.salesforce.com/services/Soap/c/29.0/" + orgId;
        soap = string.Format(@"<s:Envelope xmlns:s=""http://schemas.xmlsoap.org/soap/envelope/""><s:Body xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema""><login xmlns=""urn:enterprise.soap.sforce.com""><username>{0}</username><password>{1}</password></login></s:Body></s:Envelope>", userName, password);
        wsdlType = "enterprise";
    }
    else
    {
        url = "https://login.salesforce.com/services/Soap/u/29.0/" + orgId;
        soap = string.Format(@"<soapenv:Envelope xmlns:soapenv=""http://schemas.xmlsoap.org/soap/envelope/"" xmlns:urn=""urn:partner.soap.sforce.com""><soapenv:Body><urn:login><urn:username>{0}</urn:username><urn:password>{1}</urn:password></urn:login></soapenv:Body></soapenv:Envelope>", userName, password);
        wsdlType = "partner";
    }

    var content = new StringContent(soap, Encoding.UTF8, "text/xml");

    using (var httpClient = new HttpClient())
    {
        var request = new HttpRequestMessage();

        request.RequestUri = new Uri(url);
        request.Method = HttpMethod.Post;
        request.Content = content;

        request.Headers.Add("SOAPAction", "login");

        var responseMessage = await httpClient.SendAsync(request);
        var response = await responseMessage.Content.ReadAsStringAsync();

        if (responseMessage.IsSuccessStatusCode)
        {
            var resultXml = new XmlDocument();
            var mgr = new XmlNamespaceManager(resultXml.NameTable);

            mgr.AddNamespace("soapenv", "http://schemas.xmlsoap.org/soap/envelope/");
            mgr.AddNamespace("ns", string.Format("urn:{0}.soap.sforce.com", wsdlType));

            resultXml.LoadXml(response);

            var loginResultNode = resultXml.SelectSingleNode("//ns:loginResponse", mgr).InnerXml;

            var serializer = new XmlSerializer(typeof(T));
            var stringReader = new StringReader(loginResultNode);

            var loginResult = (T)serializer.Deserialize(stringReader);
            stringReader.Dispose();

            return loginResult;
        }

        throw new Exception("Failed login");
    }
}

LoginResult.cs

using System.Xml.Serialization;

namespace Tester.Models.Enterprise
{
    [XmlRoot(Namespace = "urn:enterprise.soap.sforce.com", ElementName = "result", IsNullable = true)]
    public class LoginResult
    {
        [XmlElement(ElementName = "metadataServerUrl")]
        public string MetadataServerUrl;

        [XmlElement(ElementName = "passwordExpired")]
        public bool PasswordExpired;

        [XmlElement(ElementName = "sandbox")]
        public bool Sandbox;

        [XmlElement(ElementName = "serverUrl")]
        public string ServerUrl;

        [XmlElement(ElementName = "sessionId")]
        public string SessionId;

        [XmlElement(ElementName = "userId")]
        public string UserId;

        [XmlElement(ElementName = "userInfo")]
        public UserInfoResult UserInfo;
    }
}

namespace Tester.Models.Partner
{
    [XmlRoot(Namespace = "urn:partner.soap.sforce.com", ElementName = "result", IsNullable = true)]
    public class LoginResult
    {
        [XmlElement(ElementName = "metadataServerUrl")]
        public string MetadataServerUrl;

        [XmlElement(ElementName = "passwordExpired")]
        public bool PasswordExpired;

        [XmlElement(ElementName = "sandbox")]
        public bool Sandbox;

        [XmlElement(ElementName = "serverUrl")]
        public string ServerUrl;

        [XmlElement(ElementName = "sessionId")]
        public string SessionId;

        [XmlElement(ElementName = "userId")]
        public string UserId;

        [XmlElement(ElementName = "userInfo")]
        public UserInfoResult UserInfo;
    }
}

loginResult.cs

var loginResult = await Login<Enterprise.LoginResult>(userName, password, orgId);

... or ...

var loginResult = await Login<Partner.LoginResult>(userName, password, orgId);

UserInfoResult.cs

using System.Xml.Serialization;

namespace Tester.Models.Enterprise
{
    [XmlRoot(Namespace = "urn:enterprise.soap.sforce.com", ElementName = "userInfo", IsNullable = true)]
    public class UserInfoResult
    {
        [XmlElement(ElementName = "accessibilityMode")]
        public bool AccessibilityMode;

        [XmlElement(ElementName = "currencySymbol")]
        public string CurrencySymbol;

        [XmlElement(ElementName = "orgAttachmentFileSizeLimit")]
        public int OrgAttachmentFileSizeLimit;

        [XmlElement(ElementName = "orgDefaultCurrencyIsoCode")]
        public string OrgDefaultCurrencyIsoCode;

        [XmlElement(ElementName = "orgDisallowHtmlAttachments")]
        public bool OrgDisallowHtmlAttachments;

        [XmlElement(ElementName = "orgHasPersonAccounts")]
        public bool OrgHasPersonAccounts;

        [XmlElement(ElementName = "organizationId")]
        public string OrganizationId;

        [XmlElement(ElementName = "organizationMultiCurrency")]
        public bool OrganizationMultiCurrency;

        [XmlElement(ElementName = "organizationName")]
        public string OrganizationName;

        [XmlElement(ElementName = "profileId")]
        public string ProfileId;

        [XmlElement(ElementName = "roleId")]
        public string RoleId;

        [XmlElement(ElementName = "sessionSecondsValid")]
        public int SessionSecondsValid;

        [XmlElement(ElementName = "userDefaultCurrencyIsoCode")]
        public string UserDefaultCurrencyIsoCode;

        [XmlElement(ElementName = "userEmail")]
        public string UserEmail;

        [XmlElement(ElementName = "userFullName")]
        public string UserFullName;

        [XmlElement(ElementName = "userId")]
        public string UserId;

        [XmlElement(ElementName = "userLanguage")]
        public string UserLanguage;

        [XmlElement(ElementName = "userLocale")]
        public string UserLocale;

        [XmlElement(ElementName = "userName")]
        public string UserName;

        [XmlElement(ElementName = "userTimeZone")]
        public string UserTimeZone;

        [XmlElement(ElementName = "userType")]
        public string UserType;

        [XmlElement(ElementName = "userUiSkin")]
        public string UserUiSkin;
    }
}

namespace Tester.Models.Partner
{
    [XmlRoot(Namespace = "urn:partner.soap.sforce.com", ElementName = "userInfo", IsNullable = true)]
    public class UserInfoResult
    {
        [XmlElement(ElementName = "accessibilityMode")]
        public bool AccessibilityMode;

        [XmlElement(ElementName = "currencySymbol")]
        public string CurrencySymbol;

        [XmlElement(ElementName = "orgAttachmentFileSizeLimit")]
        public int OrgAttachmentFileSizeLimit;

        [XmlElement(ElementName = "orgDefaultCurrencyIsoCode")]
        public string OrgDefaultCurrencyIsoCode;

        [XmlElement(ElementName = "orgDisallowHtmlAttachments")]
        public bool OrgDisallowHtmlAttachments;

        [XmlElement(ElementName = "orgHasPersonAccounts")]
        public bool OrgHasPersonAccounts;

        [XmlElement(ElementName = "organizationId")]
        public string OrganizationId;

        [XmlElement(ElementName = "organizationMultiCurrency")]
        public bool OrganizationMultiCurrency;

        [XmlElement(ElementName = "organizationName")]
        public string OrganizationName;

        [XmlElement(ElementName = "profileId")]
        public string ProfileId;

        [XmlElement(ElementName = "roleId")]
        public string RoleId;

        [XmlElement(ElementName = "sessionSecondsValid")]
        public int SessionSecondsValid;

        [XmlElement(ElementName = "userDefaultCurrencyIsoCode")]
        public string UserDefaultCurrencyIsoCode;

        [XmlElement(ElementName = "userEmail")]
        public string UserEmail;

        [XmlElement(ElementName = "userFullName")]
        public string UserFullName;

        [XmlElement(ElementName = "userId")]
        public string UserId;

        [XmlElement(ElementName = "userLanguage")]
        public string UserLanguage;

        [XmlElement(ElementName = "userLocale")]
        public string UserLocale;

        [XmlElement(ElementName = "userName")]
        public string UserName;

        [XmlElement(ElementName = "userTimeZone")]
        public string UserTimeZone;

        [XmlElement(ElementName = "userType")]
        public string UserType;

        [XmlElement(ElementName = "userUiSkin")]
        public string UserUiSkin;
    }
}