.NET code used for interacting with the SOAP and Metadata APIs without using proxy classes generated by WSDLs

CreateCustom.cs

private static async Task<string> Create(string query, string sessionId, string metadataServerUrl)
{
    var wsdlNamespace = "http://soap.sforce.com/2006/04/metadata";
    var header = "";
    var action = "create";

    var soap = string.Format(
@"<soapenv:Envelope xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" 
    xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" 
    xmlns:soapenv=""http://schemas.xmlsoap.org/soap/envelope/"" 
    xmlns:cmd=""{0}"" 
    xmlns:apex=""http://soap.sforce.com/2006/08/apex"">

    <soapenv:Header>
        <cmd:SessionHeader>
            <cmd:sessionId>{1}</cmd:sessionId>
        </cmd:SessionHeader>
        {2}
    </soapenv:Header>
    <soapenv:Body>
        <{3} xmlns=""{4}"">
            {5}
        </{6}>
    </soapenv:Body>
</soapenv:Envelope>", wsdlNamespace, sessionId, header, action, wsdlNamespace, query, action);

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

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

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

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

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

        if (responseMessage.IsSuccessStatusCode)
        {
            return response;
        }
    }

    throw new Exception("Failed create object");
}

CreateCustomField.cs

private static async Task<CreateResult> CreateCustomField(string customObject, string fieldName, string sessionId, string metadataServerUrl)
{
    var customFieldQuery = string.Format(
@"<metadata xsi:type=""CustomField"" xmlns:cmd=""http://soap.sforce.com/2006/04/metadata"">
    <fullName>{0}.{1}__c</fullName>
        <label>{1}</label>
        <length>100</length>
    <type>Text</type>
</metadata>", customObject + "__c", fieldName); // TODO: pass this in for flexibility

    var customFieldResponse = await Create(customFieldQuery, sessionId, metadataServerUrl);

    var resultXml = new XmlDocument();
    var mgr = new XmlNamespaceManager(resultXml.NameTable);

    mgr.AddNamespace("soapenv", "http://schemas.xmlsoap.org/soap/envelope/");
    mgr.AddNamespace("meta", "http://soap.sforce.com/2006/04/metadata");

    resultXml.LoadXml(customFieldResponse);

    var selectSingleNode = resultXml.SelectSingleNode("//meta:createResponse", mgr);
    if (selectSingleNode == null) return null;

    var loginResultNode = selectSingleNode.InnerXml;
    var serializer = new XmlSerializer(typeof(CreateResult));
    var stringReader = new StringReader(loginResultNode);
    var createResult = (CreateResult)serializer.Deserialize(stringReader);

    stringReader.Dispose();

    return createResult;
}

CreateCustomObject.cs

private static async Task<CreateResult> CreateCustomObject(string customObject, string sessionId, string metadataServerUrl)
{
    var customObjectQuery = string.Format(
@"<metadata xsi:type=""CustomObject"" xmlns:cmd=""http://soap.sforce.com/2006/04/metadata"">
    <fullName>{0}__c</fullName>
    <label>{0}</label>
    <pluralLabel>{0}</pluralLabel>
    <deploymentStatus>Deployed</deploymentStatus>
    <sharingModel>ReadWrite</sharingModel>
    <nameField>
        <label>ID</label>
        <type>AutoNumber</type>
    </nameField>
</metadata>", customObject);

    var customObjectResponse = await Create(customObjectQuery, sessionId, metadataServerUrl);
    var resultXml = new XmlDocument();
    var mgr = new XmlNamespaceManager(resultXml.NameTable);

    mgr.AddNamespace("soapenv", "http://schemas.xmlsoap.org/soap/envelope/");
    mgr.AddNamespace("meta", "http://soap.sforce.com/2006/04/metadata");

    resultXml.LoadXml(customObjectResponse);

    var selectSingleNode = resultXml.SelectSingleNode("//meta:createResponse", mgr);
    if (selectSingleNode == null) return null;

    var loginResultNode = selectSingleNode.InnerXml;
    var serializer = new XmlSerializer(typeof (CreateResult));
    var stringReader = new StringReader(loginResultNode);
    var createResult = (CreateResult) serializer.Deserialize(stringReader);

    stringReader.Dispose();

    return createResult;
}

HandleLoginResponse.cs

...

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;
}

...

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;
    }
}

Main.cs

private static void Main()
{
    AsyncMain().Wait();
}

static async Task AsyncMain()
{
    const string userName = "[email protected]";
    const string password = "password";
    const string orgId = "0DFi00000008UYO";
    const string customObject = "MyCustomObject";
    const string fieldName = "MyCustomField";

    var loginResultEnterprise = await Login<Enterprise.LoginResult>(userName, password, orgId);
    Console.WriteLine(loginResultEnterprise.UserId);

    var loginResultPartner = await Login<Partner.LoginResult>(userName, password, orgId);
    Console.WriteLine(loginResultPartner.UserId);

    var createObjectResult = await CreateCustomObject(customObject, loginResultPartner.SessionId, loginResultPartner.MetadataServerUrl);
    Console.WriteLine(createObjectResult.Id);

    var createFieldResult = await CreateCustomField(customObject, fieldName, loginResultPartner.SessionId, loginResultPartner.MetadataServerUrl);
    Console.WriteLine(createFieldResult.Id);
}

SoapLogin.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(
@"<soapenv:Envelope xmlns:soapenv=""http://schemas.xmlsoap.org/soap/envelope/"">
    <soapenv:Body>
        <login xmlns=""urn:enterprise.soap.sforce.com"">
            <username>{0}</username>
            <password>{1}</password>
        </login>
    </soapenv:Body>
</soapenv: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/"">
    <soapenv:Body>
        <login xmlns=""urn:partner.soap.sforce.com"">
            <username>{0}</username>
            <password>{1}</password>
        </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)
        {

        ... 

        }

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

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;
    }
}