Split of some known error cases from `fxa-client-other-error`

NoExistingAuthFlow can happen when users manually navigate through the
oauth flow URLs. Just count the errors in Glean rather than report them
to Sentry.  Use a separate label for the errors, and reserve `fxa_other`
for unexpected errors.

Handle OriginMismatch the same, which can happen when trying to pair two
firefox instances that are configured to use different servers.

BackoffError was similar, but I kept the sentry reporting for this one,
since it seems useful to see the reason for backoff errors.  Going
through the current list of backoff errors lead me to open #5918

components/fxa-client/android/metrics.yaml

@@ -41,6 +41,8 @@ fxa_client:
     labels:
       - network
       - authentication
+      - no_existing_auth_flow
+      - origin_mismatch
       - fxa_other
       - unexpected
     bugs:

components/fxa-client/android/src/main/java/mozilla/appservices/fxaclient/FxaClient.kt

@@ -513,6 +513,12 @@ class FxaClient(inner: FirefoxAccount, persistCallback: PersistCallback?) : Auto
         } catch (e: FxaException.Authentication) {
             FxaClientMetrics.errorCount["authentication"].add()
             throw e
+        } catch (e: FxaException.NoExistingAuthFlow) {
+            FxaClientMetrics.errorCount["no_existing_auth_flow"].add()
+            throw e
+        } catch (e: FxaException.OriginMismatch) {
+            FxaClientMetrics.errorCount["origin_mismatch"].add()
+            throw e
         } catch (e: FxaException) {
             FxaClientMetrics.errorCount["fxa_other"].add()
             throw e

components/fxa-client/src/error.rs

@@ -38,6 +38,12 @@ pub enum FxaError {
     /// **Note:** This error is currently only thrown in the Swift language bindings.
     #[error("the requested authentication flow was not active")]
     WrongAuthFlow,
+    /// Origin mismatch when handling a pairing flow
+    ///
+    /// The most likely cause of this is that a user tried to pair together two firefox instances
+    /// that are configured to use different servers.
+    #[error("Origin mismatch")]
+    OriginMismatch,
     /// A scoped key was missing in the server response when requesting the OLD_SYNC scope.
     #[error("The sync scoped key was missing")]
     SyncScopedKeyMissingInServerResponse,
@@ -194,17 +200,21 @@ impl GetErrorHandling for Error {
             | Error::NoRefreshToken
             | Error::NoScopedKey(_)
             | Error::NoCachedToken(_) => {
-                ErrorHandling::convert(crate::FxaError::Authentication).log_warning()
-            }
-            Error::RequestError(_) => {
-                ErrorHandling::convert(crate::FxaError::Network).log_warning()
+                ErrorHandling::convert(FxaError::Authentication).log_warning()
             }
+            Error::RequestError(_) => ErrorHandling::convert(FxaError::Network).log_warning(),
             Error::SyncScopedKeyMissingInServerResponse => {
-                ErrorHandling::convert(crate::FxaError::SyncScopedKeyMissingInServerResponse)
+                ErrorHandling::convert(FxaError::SyncScopedKeyMissingInServerResponse)
                     .report_error("fxa-client-scoped-key-missing")
             }
-            _ => ErrorHandling::convert(crate::FxaError::Other)
-                .report_error("fxa-client-other-error"),
+            Error::UnknownOAuthState => {
+                ErrorHandling::convert(FxaError::NoExistingAuthFlow).log_warning()
+            }
+            Error::BackoffError(_) => {
+                ErrorHandling::convert(FxaError::Other).report_error("fxa-client-backoff")
+            }
+            Error::OriginMismatch => ErrorHandling::convert(FxaError::OriginMismatch),
+            _ => ErrorHandling::convert(FxaError::Other).report_error("fxa-client-other-error"),
         }
     }
 }

components/fxa-client/src/fxa_client.udl

@@ -59,11 +59,8 @@ enum FxaError {
   // The application may retry at a later time once connectivity is restored.
   "Network",
 
-  // Thrown if the application attempts to complete an OAuth flow when no OAuth flow
-  // has been initiated. This may indicate a user who navigated directly to the OAuth
-  // `redirect_uri` for the application.
-  //
-  // **Note:** This error is currently only thrown in the Swift language bindings.
+  // Thrown if the application attempts to complete an OAuth flow when no OAuth flow has been initiated for that state.
+  // This may indicate a user who navigated directly to the OAuth `redirect_uri` for the application.
   "NoExistingAuthFlow",
 
   // Thrown if the application attempts to complete an OAuth flow, but the state
@@ -75,6 +72,12 @@ enum FxaError {
   // **Note:** This error is currently only thrown in the Swift language bindings.
   "WrongAuthFlow",
 
+  // Origin mismatch when handling a pairing flow
+  //
+  // The most likely cause of this is that a user tried to pair together two firefox instances
+  // that are configured to use different servers.
+  "OriginMismatch",
+
   // The sync scoped key was missing in the server response
   "SyncScopedKeyMissingInServerResponse",