feat: add secret_key config, deprecate personal_api_key

[turnipdabeets]

Problem

The credential used for local feature flag evaluation and remote config accepts either a Personal API Key (phx_...) or a Project Secret API Key (phs_...), but the config field is named personal_api_key. Passing a project secret key to a field called "personal api key" is confusing now that project secret keys exist.

Change

• Add secret_key as the canonical config field — accepts a Personal API Key or a Project Secret API Key.
• Keep personal_api_key as a deprecated alias that resolves into secret_key. Non-breaking: existing code keeps working and gets a DeprecationWarning.
• Prefer secret_key when both are provided.
• Update docstrings and user-facing error messages to reference secret_key.

Context

From the Slack discussion + PostHog/posthog-js#4046. This covers the rename only. The other two items from that thread — making flag refresh opt-in, and a config to enable/disable local eval independent of the env var — are separate.

Part of a coordinated rename across the backend SDKs (python, node, php, ruby, go, dotnet, rs).

[greptile-apps]

Comments Outside Diff (1)

1. posthog/test/test_client.py, line 69-79 (link)

   This existing test still passes personal_api_key to the constructor without wrapping it in assertWarns(DeprecationWarning). The PR's deprecation logic fires the warning whenever personal_api_key is not None and secret_key is None, which is exactly this call's shape. Any CI run with -W error::DeprecationWarning (or filterwarnings = error in pytest.ini) will fail this test. The simplest fix is to migrate the test to use secret_key directly, which is the canonical param being introduced here.

_{Reviews (1): Last reviewed commit: "feat: add secret_key config, deprecate p..." | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-07-02 16:43:01 UTC
Duration: 176690ms

✅ All Tests Passed!

46/46 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	517ms
Format Validation.Event Has Uuid	✅	1507ms
Format Validation.Event Has Lib Properties	✅	1507ms
Format Validation.Distinct Id Is String	✅	1507ms
Format Validation.Token Is Present	✅	1506ms
Format Validation.Custom Properties Preserved	✅	1507ms
Format Validation.Event Has Timestamp	✅	1506ms
Retry Behavior.Retries On 503	✅	9516ms
Retry Behavior.Does Not Retry On 400	✅	3506ms
Retry Behavior.Does Not Retry On 401	✅	3510ms
Retry Behavior.Respects Retry After Header	✅	9513ms
Retry Behavior.Implements Backoff	✅	23517ms
Retry Behavior.Retries On 500	✅	7016ms
Retry Behavior.Retries On 502	✅	7511ms
Retry Behavior.Retries On 504	✅	7507ms
Retry Behavior.Max Retries Respected	✅	23532ms
Deduplication.Generates Unique Uuids	✅	1496ms
Deduplication.Preserves Uuid On Retry	✅	7515ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	14520ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7504ms
Deduplication.No Duplicate Events In Batch	✅	1508ms
Deduplication.Different Events Have Different Uuids	✅	1506ms
Compression.Sends Gzip When Enabled	✅	1507ms
Batch Format.Uses Proper Batch Structure	✅	1507ms
Batch Format.Flush With No Events Sends Nothing	✅	1005ms
Batch Format.Multiple Events Batched Together	✅	1505ms
Error Handling.Does Not Retry On 403	✅	3509ms
Error Handling.Does Not Retry On 413	✅	3508ms
Error Handling.Retries On 408	✅	7513ms

Feature_Flags Tests

✅ 17/17 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	1003ms
Request Payload.Flags Request Uses V2 Query Param	✅	1007ms
Request Payload.Flags Request Hits Flags Path Not Decide	✅	1006ms
Request Payload.Flags Request Omits Authorization Header	✅	1006ms
Request Payload.Token In Flags Body Matches Init	✅	1006ms
Request Payload.Groups Round Trip	✅	1006ms
Request Payload.Groups Default To Empty Object	✅	1007ms
Request Payload.Disable Geoip False Propagates As Geoip Disable False	✅	1006ms
Request Payload.Disable Geoip Omitted Defaults To False	✅	1006ms
Request Payload.Flag Keys To Evaluate Contains Only Requested Key	✅	1007ms
Request Lifecycle.No Flags Request On Init Alone	✅	503ms
Request Lifecycle.No Flags Request On Normal Capture	✅	1509ms
Request Lifecycle.Two Flag Calls Produce Two Remote Requests	✅	1010ms
Request Lifecycle.Mock Response Value Is Returned To Caller	✅	1002ms
Retry Behavior.Retries Flags On 502	✅	1006ms
Retry Behavior.Retries Flags On 504	✅	1006ms
Side Effect Events.Get Feature Flag Captures Feature Flag Called Event	✅	1508ms

[greptile-apps]

_{Reviews (2): Last reviewed commit: "test: assert secret_key in wrong-key err..." | Re-trigger Greptile}