LoginActivity: startActivityForResult deprecated.

Migrate startActivityForResult/onActivityResult to
StartActivityForResult/registerForActivityResult in
LoginActivity/OAuth.

This moves responsibility for scheduling the starting Intent from
OAuth to LoginActivity.

OAuth still generates the Intent.  But instead of starting the intent
directly in OAuth, the intent is returned to LoginActivity.  This
better associates processing the activity result with its invocation.

OAuthTest module updated to accommodate internal API change.

app/src/main/java/audio/funkwhale/ffa/activities/LoginActivity.kt

@@ -5,6 +5,7 @@ import android.content.res.Configuration
 import android.net.Uri
 import android.os.Bundle
 import android.view.ViewGroup
+import androidx.activity.result.contract.ActivityResultContracts.StartActivityForResult
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.view.doOnLayout
 import androidx.lifecycle.lifecycleScope
@@ -40,26 +41,21 @@ class LoginActivity : AppCompatActivity() {
     limitContainerWidth()
   }
 
-  override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
-    super.onActivityResult(requestCode, resultCode, data)
+  private var resultLauncher =
+    registerForActivityResult(StartActivityForResult()) { result ->
+    result.data?.let {
+      oAuth.exchange(this, it) {
+        PowerPreference
+          .getFileByName(AppContext.PREFS_CREDENTIALS)
+          .setBoolean("anonymous", false)
 
-    data?.let {
-      when (requestCode) {
-        0 -> {
-          oAuth.exchange(this, data) {
-            PowerPreference
-              .getFileByName(AppContext.PREFS_CREDENTIALS)
-              .setBoolean("anonymous", false)
+        lifecycleScope.launch(Main) {
+          Userinfo.get(this@LoginActivity, oAuth)?.let {
+            startActivity(Intent(this@LoginActivity, MainActivity::class.java))
 
-            lifecycleScope.launch(Main) {
-              Userinfo.get(this@LoginActivity, oAuth)?.let {
-                startActivity(Intent(this@LoginActivity, MainActivity::class.java))
-
-                return@launch finish()
-              }
-              throw Exception(getString(R.string.login_error_userinfo))
-            }
+            return@launch finish()
           }
+          throw Exception(getString(R.string.login_error_userinfo))
         }
       }
     }
@@ -134,7 +130,7 @@ class LoginActivity : AppCompatActivity() {
     oAuth.init(hostname)
     return oAuth.register {
       PowerPreference.getFileByName(AppContext.PREFS_CREDENTIALS).setString("hostname", hostname)
-      oAuth.authorize(this)
+      resultLauncher.launch(oAuth.authorizeIntent(this))
     }
   }
 

app/src/main/java/audio/funkwhale/ffa/utils/OAuth.kt

@@ -184,11 +184,10 @@ class OAuth(private val authorizationServiceFactory: AuthorizationServiceFactory
     )
   }
 
-  fun authorize(activity: Activity) {
+  fun authorizeIntent(activity: Activity): Intent? {
     val authService = service(activity)
-    authorizationRequest()?.let { it ->
-      val intent = authService.getAuthorizationRequestIntent(it)
-      activity.startActivityForResult(intent, 0)
+    return authorizationRequest()?.let { it ->
+      authService.getAuthorizationRequestIntent(it)
     }
   }
 

app/src/test/java/audio/funkwhale/ffa/utils/OAuthTest.kt

@@ -27,6 +27,7 @@ import org.junit.Before
 import org.junit.Test
 import strikt.api.expectThat
 import strikt.api.expectThrows
+import strikt.assertions.isA
 import strikt.assertions.isEqualTo
 import strikt.assertions.isFalse
 import strikt.assertions.isNotNull
@@ -282,7 +283,7 @@ class OAuthTest {
   }
 
   @Test
-  fun `authorize() should start activity for result`() {
+  fun `authorizeIntent() should return an Intent`() {
 
     mockkStatic(PowerPreference::class)
     every { PowerPreference.getFileByName(any()) } returns mockPreference
@@ -302,9 +303,7 @@ class OAuthTest {
 
     val activity = mockk<Activity>(relaxed = true)
 
-    oAuth.authorize(activity)
-
-    verify { activity.startActivityForResult(mockkIntent, 0) }
+    expectThat(oAuth.authorizeIntent(activity)).isNotNull().isA<Intent>()
   }
 
   private fun <T> deserializeJson(