Get SharePoint user from WebApi2 Identity

Question

I have a WebApi2 endpoint where supportCredentials flag is set to true. On the IIS the Anonymous Authentication on false and the Windows Authentication on true.

What I'm trying to do is to load the right ShatePoint user based on the Identity loaded in RequestContext.Principal.Identity.

Current code:

string userLogin = RequestContext.Principal.Identity.Name;
using (ClientContext ctx = new ClientContext(WebConfig.Portal))
{
    List list = ctx.Site.RootWeb.SiteUserInfoList;

    var caml = new CamlQuery
    {
        ViewXml = $"<View><Query><Where><Contains><FieldRef Name='Name'/><Value Type='Text'>{userLogin}</Value></Contains></Where></Query></View>"
    };

    var users = list.GetItems(caml);
    ctx.Load(users);
    ctx.ExecuteQuery();

    IEnumerable<ListItem> user = from u in users.Cast<ListItem>()
                orderby u.Id descending
                select u;

    return Convert.ToString(user.First()["EMail"]);
}

It works, but I don't really like it. My first approach was:

string userLogin = RequestContext.Principal.Identity.Name;
using (ClientContext ctx = new ClientContext(WebConfig.Portal))
{
    UserCollection list = ctx.Site.RootWeb.SiteUsers;
    User user = list.GetByLoginName(userLogin);
    ctx.Load(user);
    ctx.ExecuteQuery();
    return user.Email;
}

The latter does not always work, since the Identity.Name is like "DOMAIN\USERNAME" but some SharePoint users have e.g the prefix i:0#.w| which is not present in the Identity.Name. The idea was to add i:0#.w| + userLogin, but as far I've read, this prefix may change.

Is there a clean and working way to load the correct SharePoint user with this Identity information?

Answer 1

Assuming the login name is in casual domain format DOMAIN\USERNAME, you can convert it to valid SharePoint claims format and getting user using

using SP = Microsoft.SharePoint.Client;
//...

// resolve user principal using regular login name or e-mail:
var userPrincipal = SP.Utilities.Utility.ResolvePrincipal(
  context, 
  context.Web, 
  "DOMAIN\\user", // normal login name
  SP.Utilities.PrincipalType.User,
  SP.Utilities.PrincipalSource.All,
  context.Web.SiteUsers,
  false);

context.ExecuteQuery();

// ensure that the user principal was resolved:
if (userPrincipal.Value == null)
  throw new Exception("The specified user principal could not be resolved");

// get a User instance based on the encoded login name from userPrincipal
var user = context.Web.SiteUsers.GetByLoginName(userPrincipal.LoginName);
context.Load(user);

context.ExecuteQuery();

On the other hand, simply doing this might work for DOMAIN\USERNAME as well, so it's worth a try.

var ctx = new ClientContext(site);
var rootWeb = ctx.Site.RootWeb;
var usr = rootWeb.EnsureUser("DOMAIN\\USERNAME");
ctx.Load(usr);
ctx.ExecuteQuery();