Resource not found for the segment 'me' - azure

Question

i'm using Graph API to retrieve profile information of user who's currently logged in from the Azure AD, unfortunately i'm receiving the following error message :
{"odata.error":{"code":"Request_ResourceNotFound","message":{"lang":"en","value":"Resource not found for the segment 'me'."}}}
Below is my code :
Uri serviceRoot = new Uri(serviceRootURL);
ActiveDirectoryClient adClient = new ActiveDirectoryClient(
serviceRoot,
async () => await GetAppTokenAsync());
var user = (User)await adClient.Me
.Expand(x => x.Manager)
.ExecuteAsync();
And below is my code for GetAppTokenAsync() :
private static async Task<string> GetAppTokenAsync()
{
// Instantiate an AuthenticationContext for my directory (see authString above).
AuthenticationContext authenticationContext = new AuthenticationContext(authString, false);
// Create a ClientCredential that will be used for authentication.
// This is where the Client ID and Key/Secret from the Azure Management Portal is used.
ClientCredential clientCred = new ClientCredential(clientID, clientSecret);
// Acquire an access token from Azure AD to access the Azure AD Graph (the resource)
// using the Client ID and Key/Secret as credentials.
AuthenticationResult authenticationResult = await authenticationContext.AcquireTokenAsync(resAzureGraphAPI, clientCred);
// Return the access token.
return authenticationResult.AccessToken;
}

Answer 1

From your code "await GetAppTokenAsync()" , you are getting an app-only token , which using application identity, instead of as a user's identity .
The "(User)await adClient.Me" won't work if that token is not associated with a user .
To use app token to get user manager information ,you need to specify the user you want to query , code below is for your reference :
try
{
User manager = (User)await adClient.Users.GetByObjectId("5eba8883-c258-45d0-8add-a286a1ec1e91").Manager.ExecuteAsync();
}
catch (Exception ex)
{
throw;
}
Update
You could use authorization code flow for delegated permissions(user's identity) . If you want a client library code sample , you could refer to this code sample . After user sign in , you could use below code to get manager of current login user :
ActiveDirectoryClient client = AuthenticationHelper.GetActiveDirectoryClient();
User manager = (User)await client.Me.Manager.ExecuteAsync();

Answer 2

I used an application identity with the legacy Azure Active Directory api and the 'Application.ReadWrite.OwnedBy' permission to work around the Resource not found for the segment 'me' error. The same permission exists in the Microsoft Graph api, but the behavior is not identical. More information here.