/// <summary>
/// Acquires security token without asking for user credential.
/// </summary>
/// <param name="ctx">Authentication context instance</param>
/// <param name="resource">Identifier of the target resource that is the recipient of the requested token.</param>
/// <param name="clientCredential">The client credential to use for token acquisition.</param>
/// <param name="userId">Identifier of the user token is requested for. This parameter can be <see cref="UserIdentifier"/>.Any.</param>
/// <returns>It contains Access Token, its expiration time, user information. If acquiring token without user credential is not possible, the method throws AdalException.</returns>
public static async Task <AuthenticationResult> AcquireTokenSilentAsync(this AuthenticationContext ctx,
string resource,
ClientCredential clientCredential, UserIdentifier userId)
{
return(await ctx.AcquireTokenSilentCommonAsync(resource, new ClientKey(clientCredential), userId, null)
.ConfigureAwait(false));
}