Which HTTP response should you send?

You develop a web API named WebApi1.

When validating a token received from a client application, WebApi1 receives a MsalUiRequiredException exception from Azure Active Directory (Azure AD).

You need to formulate the response that WebApi1 will return to the client application.

Which HTTP response should you send?
A . HTTP 307 Temporary Redirect
B . HTTP 400 Bad Request
C . HTTP 403 Forbidden
D . HTTP 412 Precondition Failed

View Answer

Answer: D

Explanation:

The HyperText Transfer Protocol (HTTP) 412 Precondition Failed client error response code indicates that access to the target resource has been denied. This happens with conditional requests on methods other than GET or HEAD when the condition defined by the If-Unmodified-Since or If-None-Match headers is not fulfilled. In that case, the request, usually an upload or a modification of a resource, cannot be made and this error response is sent back.

MsalUiRequiredException

The "Ui Required" is proposed as a specialization of MsalServiceException named MsalUiRequiredException. This means you have attempted to use a non-interactive method of acquiring a token (e.g. AcquireTokenSilent), but MSAL could not do it silently. this can be because:

– you need to sign-in

– you need to consent

– you need to go through a multi-factor authentication experience.

The remediation is to call AcquireTokenInteractive

try

{

app.AcquireTokenXXX(scopes, account)

.WithYYYY(…)

.ExecuteAsync()

}

catch(MsalUiRequiredException ex)

{

app.AcquireTokenInteractive(scopes)

.WithAccount(account)

.WithClaims(ex.Claims)

.ExcecuteAsync();

}

Incorrect Answers:

A: A 307 Temporary Redirect message is an HTTP response status code indicating that the requested resource has been temporarily moved to another URI , as indicated by the special Location header returned within the response

B: The 400 Bad Request Error is an HTTP response status code that indicates that the server was unable to process the request sent by the client due to invalid syntax.

C: The 403 Forbidden Error happens when the web page (or other resource) that you’re trying to open in your web browser is a resource that you’re not allowed to access.

References: https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-handling-exceptions

https://docs.microsoft.com/en-us/azure/active-directory/develop/msal-handling-exceptions

https://github.com/AzureAD/microsoft-authentication-library-for-dotnet/wiki/exceptions