Midas Midas - 4 months ago 120
C# Question

Azure AD OAuth2 Access Token Request Error - 400 Bad Request

My WPF desktop application (C#) is attempting to read the user's Outlook emails through the Microsoft Graph API. I am stuck in the authentication process; I've already received an authentication code and now I'm trying to get an access token from Azure but keep getting a HTTP 400 error code when sending out the request for the access token:

/**** Auth Code Retrieval ****/
string authCodeUrl = "https://login.microsoftonline.com/common/oauth2/authorize";
authCodeUrl += "?client_id" = clientId;
authCodeUrl += "&redirect_uri=" + redirectUri;
authCodeUrl += "&response_type=code";
authCodeUrl += "&resource=https%3A%2F%2Fgraph.microsoft.com%2F";
Process.start(authUrl); // User logs in, we get the auth code after login
string code = "......"; // Hidden for this post

/**** Access Token Retrieval ****/
string tokenUrl = "https://login.microsoftonline.com/common/oauth2/token"
string content = "grant_type=authorization_code";
content += "&client_id=" + clientId;
content += "&resource=https%3A%2F%2Fgraph.microsoft.com%2F";
content += "&code=" + code;
content += "&redirect_uri=" + redirectUri;
WebRequest request = WebRequest.Create(tokenUrl);
request.ContentType = "application/x-www-form-urlencoded";
byte[] data = Encoding.UTF8.GetBytes(content);
request.ContentLength = data.Length;
request.Method = "POST";
try
{
using (Stream stream = request.GetRequestStream())
{
stream.Write(data, 0, data.Length);
}
WebResponse response = request.GetResponse(); // This throws exception
}
catch (Exception error) // This catches the exception
{
Console.WriteLine(error.Message); // Outputs 400, bad request
}


The above is the code used to retrieve the auth code followed by the attempt to retrieve the access token. We do not have a client_secret because secrets are only for Web applications and this is a native desktop WPF application. I have read that this isn't an issue though. I have followed many tutorials and official docs online, mainly the official Graph authorization doc and I still cannot figure out what I am doing wrong. Any help would be greatly appreciated, thank you.

Answer

I used fiddler to debug the request and I found the full error message: The user or administrator has not consented to use the application. I googled this message for a bit and found some stack articles and github issue threads that lead me to the solution: my request had been using "common", in the base URL, as the tenant ID when actually I needed to use my Azure tenant ID which I acquired through this answer on stack. My new base URL for the authentication requests now looks like:

https://login.microsoftonline.com/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/oauth2/authorize 

where "xxxx-....xxx" would be replaced by your Azure tenant id!

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