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feat(posthog_client): support feature flag secure API (#12201)

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## Problem

Part of #11813 

PostHog has two endpoints to retrieve feature flags: the old project ID
one that uses personal API token, and the new one using a special
feature flag secure token that can only retrieve feature flag. The new
API I added in this patch is not documented in the PostHog API doc but
it's used in their Python SDK.

## Summary of changes

Add support for "feature flag secure token API". The API has no way of
providing a project ID so we verify if the retrieved spec is consistent
with the project ID specified by comparing the `team_id` field.

---------

Signed-off-by: Alex Chi Z <chi@neon.tech>
This commit is contained in:
Alex Chi Z.
2025-06-13 15:22:02 +08:00
committed by GitHub
parent e83f1d8ba5
commit 3046c307da
2 changed files with 58 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
libs/posthog_client_lite/src/background_loop.rs
View File

@@ -55,9 +55,16 @@ impl FeatureResolverBackgroundLoop {
continue;
}
};
let feature_store = FeatureStore::new_with_flags(resp.flags);
this.feature_store.store(Arc::new(feature_store));
tracing::info!("Feature flag updated");
let project_id = this.posthog_client.config.project_id.parse::<u64>().ok();
match FeatureStore::new_with_flags(resp.flags, project_id) {
Ok(feature_store) => {
this.feature_store.store(Arc::new(feature_store));
tracing::info!("Feature flag updated");
}
Err(e) => {
tracing::warn!("Cannot process feature flag spec: {}", e);
}
}
}
tracing::info!("PostHog feature resolver stopped");
}

59
libs/posthog_client_lite/src/lib.rs
View File

@@ -39,6 +39,9 @@ pub struct LocalEvaluationResponse {
#[derive(Deserialize)]
pub struct LocalEvaluationFlag {
#[allow(dead_code)]
id: u64,
team_id: u64,
key: String,
filters: LocalEvaluationFlagFilters,
active: bool,
@@ -107,17 +110,32 @@ impl FeatureStore {
}
}
pub fn new_with_flags(flags: Vec<LocalEvaluationFlag>) -> Self {
pub fn new_with_flags(
flags: Vec<LocalEvaluationFlag>,
project_id: Option<u64>,
) -> Result<Self, &'static str> {
let mut store = Self::new();
store.set_flags(flags);
store
store.set_flags(flags, project_id)?;
Ok(store)
}
pub fn set_flags(&mut self, flags: Vec<LocalEvaluationFlag>) {
pub fn set_flags(
&mut self,
flags: Vec<LocalEvaluationFlag>,
project_id: Option<u64>,
) -> Result<(), &'static str> {
self.flags.clear();
for flag in flags {
if let Some(project_id) = project_id {
if flag.team_id != project_id {
return Err(
"Retrieved a spec with different project id, wrong config? Discarding the feature flags.",
);
}
}
self.flags.insert(flag.key.clone(), flag);
}
Ok(())
}
/// Generate a consistent hash for a user ID (e.g., tenant ID).
@@ -534,6 +552,13 @@ impl PostHogClient {
})
}
/// Check if the server API key is a feature flag secure API key. This key can only be
/// used to fetch the feature flag specs and can only be used on a undocumented API
/// endpoint.
fn is_feature_flag_secure_api_key(&self) -> bool {
self.config.server_api_key.starts_with("phs_")
}
/// Fetch the feature flag specs from the server.
///
/// This is unfortunately an undocumented API at:
@@ -547,10 +572,22 @@ impl PostHogClient {
) -> anyhow::Result<LocalEvaluationResponse> {
// BASE_URL/api/projects/:project_id/feature_flags/local_evaluation
// with bearer token of self.server_api_key
let url = format!(
"{}/api/projects/{}/feature_flags/local_evaluation",
self.config.private_api_url, self.config.project_id
);
// OR
// BASE_URL/api/feature_flag/local_evaluation/
// with bearer token of feature flag specific self.server_api_key
let url = if self.is_feature_flag_secure_api_key() {
// The new feature local evaluation secure API token
format!(
"{}/api/feature_flag/local_evaluation",
self.config.private_api_url
)
} else {
// The old personal API token
format!(
"{}/api/projects/{}/feature_flags/local_evaluation",
self.config.private_api_url, self.config.project_id
)
};
let response = self
.client
.get(url)
@@ -803,7 +840,7 @@ mod tests {
fn evaluate_multivariate() {
let mut store = FeatureStore::new();
let response: LocalEvaluationResponse = serde_json::from_str(data()).unwrap();
store.set_flags(response.flags);
store.set_flags(response.flags, None).unwrap();
// This lacks the required properties and cannot be evaluated.
let variant =
@@ -873,7 +910,7 @@ mod tests {
let mut store = FeatureStore::new();
let response: LocalEvaluationResponse = serde_json::from_str(data()).unwrap();
store.set_flags(response.flags);
store.set_flags(response.flags, None).unwrap();
// This lacks the required properties and cannot be evaluated.
let variant = store.evaluate_boolean_inner("boolean-flag", 1.00, &HashMap::new());
@@ -929,7 +966,7 @@ mod tests {
let mut store = FeatureStore::new();
let response: LocalEvaluationResponse = serde_json::from_str(data()).unwrap();
store.set_flags(response.flags);
store.set_flags(response.flags, None).unwrap();
// This lacks the required properties and cannot be evaluated.
let variant =