Fix pressing back on AuthenticationFragment

If login request isn't disabled when user presses
back then they might get navigated back to
authentication again.

app/src/main/java/gq/kirmanak/mealient/extensions/FragmentExtensions.kt

@@ -0,0 +1,30 @@
+package gq.kirmanak.mealient.extensions
+
+import androidx.activity.OnBackPressedDispatcher
+import androidx.activity.addCallback
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.lifecycleScope
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.callbackFlow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.launch
+
+fun Fragment.executeOnceOnBackPressed(action: () -> Unit) {
+    val onBackPressedDispatcher = requireActivity().onBackPressedDispatcher
+    lifecycleScope.launch {
+        onBackPressedDispatcher.backPressedFlow().first()
+        action()
+        onBackPressedDispatcher.onBackPressed() // Execute other callbacks now
+    }
+}
+
+@OptIn(ExperimentalCoroutinesApi::class)
+fun OnBackPressedDispatcher.backPressedFlow(): Flow<Unit> = callbackFlow {
+    val callback = addCallback { trySend(Unit) }
+    awaitClose {
+        callback.isEnabled = false
+        callback.remove()
+    }
+}