PreferenceBaseActivity: Only attempt to use device credential auth on…

… API >=30

Previous Android versions do not support it.

Issue: #93

Signed-off-by: Andrew Gunnerson <accounts+github@chiller3.com>

app/src/main/java/com/chiller3/rsaf/PreferenceBaseActivity.kt

@@ -217,8 +217,14 @@ abstract class PreferenceBaseActivity : AppCompatActivity() {
     private fun startBiometricAuth() {
         Log.d(tag, "Starting biometric authentication")
 
+        val deviceCredential = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+            Authenticators.DEVICE_CREDENTIAL
+        } else {
+            0
+        }
+
         val promptInfo = BiometricPrompt.PromptInfo.Builder()
-            .setAllowedAuthenticators(Authenticators.BIOMETRIC_STRONG or Authenticators.DEVICE_CREDENTIAL)
+            .setAllowedAuthenticators(Authenticators.BIOMETRIC_STRONG or deviceCredential)
             .setTitle(getString(R.string.biometric_title))
             .build()