fix(cdk): improve OAuth error messages in DeclarativeOauth2Authenticator

[devin-ai-integration]

Summary

Improves user-facing error and warning messages in DeclarativeOauth2Authenticator by removing internal class name leakage ("OAuthAuthenticator") and replacing vague language with specific, actionable descriptions.

All changes are string-only — no logic or control flow changes.

Method	Before	After
get_client_secret() (warning)	"OAuthAuthenticator was unable to evaluate client_secret parameter hence it'll be empty"	"OAuth client_secret resolved to an empty value. If this is unexpected, verify the 'client_secret' in your connector configuration."
get_client_id()	"OAuthAuthenticator was unable to evaluate client_id parameter"	"OAuth client_id resolved to an empty value. Verify the 'client_id' in your connector configuration."
get_token_refresh_endpoint()	"OAuthAuthenticator was unable to evaluate token_refresh_endpoint parameter"	"OAuth token refresh endpoint resolved to an empty value. Verify the 'token_refresh_endpoint' in your connector configuration."
__post_init__() (3 validators)	"OAuthAuthenticator configuration error: ..."	"OAuth configuration is missing/incomplete. ..."

Resolves https://github.com/airbytehq/airbyte-internal-issues/issues/16098
Related to https://github.com/airbytehq/oncall/issues/11312

Review & Testing Checklist for Human

• Verify no downstream code matches on old error strings: Grep airbyte and airbyte-platform-internal repos for "OAuthAuthenticator was unable" or "OAuthAuthenticator configuration error" to confirm nothing catches these ValueError messages by string content.
• Verify the client_secret warning stays as warning-only: The issue notes that some APIs (e.g., Bing Ads public client OAuth) legitimately allow empty client_secret. Confirm that keeping this as logger.warning() rather than raising an exception is the correct behavior.
• Spot-check message quality: Confirm the new messages are clear to a non-technical user and follow the writing-good-error-messages guidelines.

Notes

• The client_secret empty case is intentionally kept as a warning (not an error) because public OAuth client flows legitimately omit client_secret. This is unchanged behavior — only the message text was improved.
• All 29 existing OAuth unit tests pass. No tests asserted on the old message strings.
• This is a CDK-level fix, not a connector-level fix — no connector version bump needed.

Link to Devin session: https://app.devin.ai/sessions/e66ccb78189644d2a21651edfd6e08e5

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[github-actions]

👋 Greetings, Airbyte Team Member!

Here are some helpful tips and reminders for your convenience.

💡 Show Tips and Tricks

Testing This CDK Version

You can test this version of the CDK using the following:

# Run the CLI from this branch:
uvx 'git+https://github.com/airbytehq/airbyte-python-cdk.git@devin/1774353383-improve-oauth-error-messages#egg=airbyte-python-cdk[dev]' --help

# Update a connector to use the CDK from this branch ref:
cd airbyte-integrations/connectors/source-example
poe use-cdk-branch devin/1774353383-improve-oauth-error-messages

PR Slash Commands

Airbyte Maintainers can execute the following slash commands on your PR:

• /autofix - Fixes most formatting and linting issues
• /poetry-lock - Updates poetry.lock file
• /test - Runs connector tests with the updated CDK
• /prerelease - Triggers a prerelease publish with default arguments
• /poe build - Regenerate git-committed build artifacts, such as the pydantic models which are generated from the manifest JSON schema in YAML.
• /poe <command> - Runs any poe command in the CDK environment

📚 Show Repo Guidance

Helpful Resources

• CDK API Reference

📝 Edit this welcome message.

[github-actions]

PyTest Results (Fast)

3 934 tests  ±0   3 923 ✅ +1   7m 25s ⏱️ +16s
    1 suites ±0      11 💤  - 1 
    1 files   ±0       0 ❌ ±0 

Results for commit 08093ab. ± Comparison against base commit 0e57414.

[github-actions]

PyTest Results (Full)

3 937 tests  ±0   3 925 ✅ ±0   11m 13s ⏱️ -1s
    1 suites ±0      12 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 08093ab. ± Comparison against base commit 0e57414.