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UI API called on a background thread iOS 13 using Legacy Authentication

After update to Auth0.swift version 1.17.1, The app started to throw the exception:

=================================================================
Main Thread Checker: UI API called on a background thread: -[UIViewController presentingViewController]
PID: 1180, TID: 314715, Thread name: (none), Queue name: NSOperationQueue 0x10b2210b0 (QOS: UNSPECIFIED), QoS: 0
Backtrace:
4 Auth0 0x00000001088be3dc $s5Auth013SafariWebAuthC03newB0_8callbackSo22SFSafariViewControllerC_yAA6ResultOyAA11CredentialsCGct10Foundation3URLV_yALctFyALcfU_ + 192
5 Auth0 0x000000010889e99c $s5Auth04PKCEV11credentials4from8callbackySDyS2SG_yAA6ResultOyAA11CredentialsCGctFyALcfU_ + 640
6 Auth0 0x00000001088a2f64 $s5Auth06ResultOyAA11CredentialsCGIegg_AFIegn_TR + 36
7 Auth0 0x000000010888ad9c $s5Auth020authenticationObject4from8callbackyAA8ResponseVyAA19AuthenticationErrorCG_yAA6ResultOyxGXEtAA17JSONObjectPayloadRzlFAA11CredentialsC_Tg5 + 332
8 Auth0 0x00000001088b2a70 $s5Auth07RequestV5startyyyAA6ResultOyxGcFy10Foundation4DataVSg_So13NSURLResponseCSgs5Error_pSgtcfU_AA11CredentialsC_AA014AuthenticationH0CTg5 + 280
9 Auth0 0x00000001088b5398 $s5Auth07RequestV5startyyyAA6ResultOyxGcFy10Foundation4DataVSg_So13NSURLResponseCSgs5Error_pSgtcfU_AA11CredentialsC_AA014AuthenticationH0CTg5TA + 32
10 Auth0 0x00000001088b2d6c $s10Foundation4DataVSgSo13NSURLResponseCSgs5Error_pSgIegggg_So6NSDataCSgAGSo7NSErrorCSgIeyByyy_TR + 148
11 Sonic-Inhouse 0x00000001039e7a30 __SplunkNSCFURLSessionDataTaskWithRequestCompletionHandler_block_invoke + 460
12 Dynatrace 0x0000000105e810ec __74-[DTXURLSessionInstrumentation dataTaskWithRequest_DTX:completionHandler:]_block_invoke + 792
13 CFNetwork 0x00000001be1aad7c CFNetServiceBrowserSearchForServices + 93016
14 CFNetwork 0x00000001be1bb2b0 _CFHTTPMessageSetResponseProxyURL + 9540
15 Foundation 0x00000001bb35d65c 32C04A3C-D431-351A-AE6A-1D87EE3CFFB6 + 1132124
16 Foundation 0x00000001bb267448 32C04A3C-D431-351A-AE6A-1D87EE3CFFB6 + 123976
17 Foundation 0x00000001bb35f8e4 32C04A3C-D431-351A-AE6A-1D87EE3CFFB6 + 1140964
18 Foundation 0x00000001bb2670e0 32C04A3C-D431-351A-AE6A-1D87EE3CFFB6 + 123104
19 Foundation 0x00000001bb3602dc 32C04A3C-D431-351A-AE6A-1D87EE3CFFB6 + 1143516
20 Foundation 0x00000001bb35fda8 32C04A3C-D431-351A-AE6A-1D87EE3CFFB6 + 1142184
21 libdispatch.dylib 0x000000010af11298 _dispatch_block_async_invoke2 + 104
22 libdispatch.dylib 0x000000010af02c04 _dispatch_client_callout + 16
23 libdispatch.dylib 0x000000010af05808 _dispatch_continuation_pop + 524
24 libdispatch.dylib 0x000000010af04c88 _dispatch_async_redirect_invoke + 624
25 libdispatch.dylib 0x000000010af14168 _dispatch_root_queue_drain + 376
26 libdispatch.dylib 0x000000010af14a90 _dispatch_worker_thread2 + 156
27 libsystem_pthread.dylib 0x00000001bacb5f64 _pthread_wqthread + 212
28 libsystem_pthread.dylib 0x00000001bacb8ae0 start_wqthread + 8

=================================================================

The implementation:

func login(params: [String: Any], completion: @escaping (BFFAuthenticable.AuthResult) -> Void) {
    var auth = Auth0
        .webAuth(
            clientId: clientId,
            domain: domain)
        .scope("openid offline_access") //offline_access is required for refresh token...
        .audience(audience)
    let auth0Params: [String: String] = [
        "connection": connection,
        "flow": "login",
        "prompt": "login"
    ]
    
    
    auth = auth.parameters(auth0Params)
    
    if #available(iOS 11.0, *) {
        //Prevent ios 11 from showing a prompt by using `SFSafariViewController` vs. `SFAuthenticationSession`
        auth = auth.useLegacyAuthentication()
    }
    
    auth.start {
        result in
        self.handle(result, completion: completion)
    }
}

Hey there @Eduardo.Rodrigues!

We can start digging into that but opening an issue in Auth0.swift repo will be more effective as you will be able to work directly with repo maintainers. Let us know if that works for you otherwise we’ll start digging!

Thank you, I opened an issue there already.

Perfect! Can you share the link to the issue here so that other who will encounter such issue can also track it?

Sure… this is the issue https://github.com/auth0/Auth0.swift/issues/308

Thanks a lot for that!

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