[daft2]

Changes

On Android, the root cause of SDK failures such as TLS errors never reaches JS. Auth0.Android keeps it as the exception's cause. The bridge rejects with only the top-level message, and React Native's PromiseImpl does not forward cause messages. On iOS, Auth0.swift appends the underlying error to every message, so the same failure can be diagnosed there and not on Android. Details are in #1685.

This PR adds a private helper in A0Auth0Module.kt, withUnderlyingCause(message, error). It walks the cause chain, skips the SDK's own wrappers (Auth0Exception and subclasses), and appends the first remaining throwable as CAUSE: <Throwable.toString()>. It is applied to:

• the fallback and isNetworkError branches of handleError (webAuth, resumeWebAuthSession, webAuthLogout, customTokenExchange)
• the credentials-manager rejects in getCredentials, saveCredentials, getApiCredentials and getSSOCredentials

For a TLS failure during the code exchange, the message changes:

- Something went wrong. CAUSE: Failed with unknown error
+ Something went wrong. CAUSE: Failed with unknown error. CAUSE: javax.net.ssl.SSLHandshakeException: java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.

What stays the same:

• No public API change: codes and the JS type mapping are unchanged, as are the cancelled, browser-not-available and ID-token-validation branches of handleError.
• The existing message is kept as the prefix.
• Errors without a non-SDK cause keep exactly the same message as today. That covers Auth0 API error responses, such as access_denied or an invalid refresh token.

a0.network_error used to always carry the fixed message Network error. It now gains the cause too, e.g. Network error. CAUSE: java.net.SocketTimeoutException: timeout, so only apps comparing the full message for equality would notice.

Messages that do change also gain the cause's class name and text. For network errors (a0.network_error and credentials-manager NO_NETWORK) that can include the tenant hostname, e.g. java.net.UnknownHostException: Unable to resolve host "<tenant>". It never includes tokens, which matches what iOS already exposes.

The added text is diagnostic data, not display-safe copy. It is the lower-level exception's own text and is not redacted. For example, a response-parsing failure would carry Gson's message, and some of those quote an offending value. Auth0.swift documents its messages the same way ("meant for debugging only"). Apps that forward error messages to telemetry or show them in UI should apply their own redaction, which was already advisable on iOS.

References

• Closes Android: TLS failures during token exchange and credential renewal reach JS without their cause #1685
• Provide error description in android #751: added CAUSE: to Android messages to match iOS. This continues that work.
• Bug Report: Auth0 SDK Fails on Android Emulator with a0.sdk.internal_error.unknown #1001: likely the same Android-only a0.sdk.internal_error.unknown on a TLS-intercepting network, closed without a clear cause.
• Token refresh failure reason unclear Auth0.Android#747: the advice there was to read cause, which React Native apps cannot do today.

Testing

• ./gradlew :react-native-auth0:compileDebugKotlin (from example/android) builds successfully.

• yarn typecheck, yarn lint and yarn test pass (728 tests). There are no JS changes.

• No unit tests are added. The repo has no Android unit-test setup, and adding one means new Gradle dependencies, which I didn't want to do without asking. A JS test would not exercise this Kotlin path.

• I have not run this on a device. The change was verified by reading the Auth0.Android 3.21.1 sources (AuthenticationAPIClient error adapter, SecureCredentialsManager renew callbacks, NetworkErrorException), which show the cause chain each path produces. To check manually: run the example app behind an HTTPS-intercepting proxy whose CA the app does not trust (e.g. mitmproxy, with its CA installed as a user CA so Custom Tabs can load Universal Login), log in, and inspect the rejected error's message.

• This change adds unit test coverage

• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines
• All existing and new tests complete without errors
• All active GitHub checks have passed

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• android/src/main/java/com/auth0/react/A0Auth0Module.kt

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Improved authentication error messages by including the underlying cause when available.
  • Enhanced details for credential-manager failures, network errors, and other authentication failures while preserving existing messages for unaffected error scenarios.

Android error messages now include the first cause that is not an Auth0Exception, when one exists. The change applies to authentication and credential-manager failures. Error codes and types remain unchanged.

Changes: Android error reporting

Layer / File(s)	Summary
Format errors with underlying causes android/src/main/java/com/auth0/react/A0Auth0Module.kt	The module traverses the exception cause chain and appends the first non-Auth0Exception cause to error messages. Authentication and credential-manager failures use this formatting. Existing messages are preserved when no such cause exists. Punctuation is normalized before appending the cause.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: subhankarmaiti

Merge Risk: ⚪ Minimal · up to 265ec

Android’s added cause details reach the public error messages on the inspected paths. No merge-blocking issue remains after normal checks.

Security architecture risk: 🔵 Low · up to 62603

Additional diagnostic text reaches application JavaScript, while error codes and existing authentication error handling remain unchanged. No new privilege or cross-tenant access was identified. The main uncertainty is whether lower-level exception messages contain data unsuitable for display or forwarding.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The demonstrated exposure increase is additional failure information delivered to the calling application's JavaScript. The inspected change does not add an external recipient, service authority, or cross-tenant operation; application-specific redistribution of errors remains outside the inspected scope.

Trust Boundaries and Controls

• observed — The new formatter filters exception types but does not redact the selected exception text. Authentication response parsing is one eligible producer, so the added text cannot be classified as TLS-only. The inspected sources do not establish a concrete secret-bearing message reaching an unauthorized recipient.

Hardening Proposals

• proposed — Document cause-enriched messages as diagnostic data rather than guaranteed display-safe text. Applications forwarding these messages to telemetry or user interfaces should apply an appropriate redaction policy; separating safe display text from detailed diagnostics is an optional stronger boundary.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 11.11% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly summarizes the main change: Android error messages now include underlying causes to match iOS behavior.
Linked Issues check		Issue #1685 requires Android errors to expose the underlying TLS cause while preserving the error code and JS type. The diff adds withUnderlyingCause and applies it to the authentication fallback, n…
Out of Scope Changes check		The diff changes only error-message construction in A0Auth0Module.kt. Applying the same cause reporting to the related network and credentials-manager paths supports consistent Android error diagnos…
Description check		The pull request description directly explains the Android error-message changes, affected code paths, preserved behavior, references, and testing performed.

Full details: Linked Issues check

Explanation

Issue #1685 requires Android errors to expose the underlying TLS cause while preserving the error code and JS type. The diff adds withUnderlyingCause and applies it to the authentication fallback, network-error, and credentials-manager rejection paths, including getCredentials. It skips Auth0Exception wrappers and appends the first non-SDK cause. The rejection codes and original throwable arguments remain unchanged. The issue does not require new tests.

Full details: Out of Scope Changes check

Explanation

The diff changes only error-message construction in A0Auth0Module.kt. Applying the same cause reporting to the related network and credentials-manager paths supports consistent Android error diagnosis. No unrelated changes appear in the diff.

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Inline comments:
Review comments at @android/src/main/java/com/auth0/react/A0Auth0Module.kt:
- Around line 1072-1090: Update the isNetworkError branch in handleError to pass
withUnderlyingCause("Network error", error) as the rejection message while
preserving the existing error code and throwable argument, so wrapped socket,
timeout, and DNS causes reach JavaScript.

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