docs(auth): document intentional session-style NIP-98 model

Co-authored-by: userAdityaa <aditya.chaudhary1558@gmail.com>
Co-committed-by: userAdityaa <aditya.chaudhary1558@gmail.com>

backend/README.md

@@ -60,7 +60,13 @@ See [spec](spec) for more details
 
 ## API Routes
 
-All routes are NIP-98 protected.
+Most API routes are NIP-98 protected.
+
+Public exceptions:
+
+- `GET /plans`
+- `GET /plans/:id`
+- `POST /stripe/webhook` (validated with Stripe signatures instead)
 
 - `GET /identity` — get auth identity (`pubkey`, `is_admin`)
 - `GET /tenants` — list tenants (admin)
@@ -73,3 +79,13 @@ All routes are NIP-98 protected.
 - `PUT /relays/:id` — update relay (admin or relay tenant)
 - `POST /relays/:id/deactivate` — deactivate relay (admin or relay tenant)
 - `GET /invoices` — list invoices (`?tenant=<pubkey>` allowed for admin only)
+
+## API Auth Model
+
+Caravel intentionally uses a session-style variant of NIP-98 for client-to-backend API auth.
+
+- Frontend signs one kind `27235` event with `u = VITE_API_URL` and caches that header for about 10 minutes.
+- Backend verifies event kind, signature, and that `u` contains configured `HOST`.
+- Backend intentionally does not bind auth to exact request URL/method/query, and does not enforce payload hash, timestamp freshness window, or replay cache.
+- Goal: reduce repeated wallet signing prompts and avoid cookie-based sessions.
+- Tradeoff: this is weaker request-intent binding than strict NIP-98 semantics.

backend/spec/api.md

@@ -184,9 +184,11 @@ Notes:
 ## `extract_auth_pubkey(&self, headers: &HeaderMap) -> Result<String>`
 
 - Parses `Authorization` header
-- Validates event kind and signature using `nostr_sdk`
+- Validates event kind (`27235`) and signature using `nostr_sdk`
-- Validates event `u` against `HOST` (not the request path. Non-standard, but correct)
+- Validates event `u` contains configured `HOST`
-- Does not validate `method` tag
+- Intentionally does **not** enforce exact request URL/method/query matching
+- Intentionally does **not** validate `payload` tag/hash, `created_at` freshness window, or replay nonce/cache
+- This is a deliberate session-style tradeoff to reduce repeated signer prompts in the client
 - Returns pubkey if header all checks pass
 
 Refer to https://github.com/nostr-protocol/nips/blob/master/98.md for details. Use `nostr_sdk` functionality where possible.

backend/src/api.rs

@@ -12,7 +12,7 @@ use base64::Engine;
 use nostr_sdk::{Event, JsonUtil, Kind};
 use serde::{Deserialize, Serialize};
 
-use crate::billing::Billing;
+use crate::billing::{Billing, InvoiceLookupError};
 use crate::command::Command;
 use crate::models::{
     RELAY_STATUS_ACTIVE, RELAY_STATUS_DELINQUENT, RELAY_STATUS_INACTIVE, Relay, Tenant,
@@ -72,6 +72,11 @@ enum ApiError {
     Unauthorized(anyhow::Error),
     Forbidden(&'static str),
     NotFound(&'static str),
+    Client {
+        status: StatusCode,
+        code: &'static str,
+        message: &'static str,
+    },
     Internal(String),
 }
 
@@ -81,11 +86,36 @@ impl IntoResponse for ApiError {
             Self::Unauthorized(e) => err(StatusCode::UNAUTHORIZED, "unauthorized", &e.to_string()),
             Self::Forbidden(message) => err(StatusCode::FORBIDDEN, "forbidden", message),
             Self::NotFound(message) => err(StatusCode::NOT_FOUND, "not-found", message),
+            Self::Client {
+                status,
+                code,
+                message,
+            } => err(status, code, message),
             Self::Internal(message) => err(StatusCode::INTERNAL_SERVER_ERROR, "internal", &message),
         }
     }
 }
 
+fn map_invoice_lookup_error(error: InvoiceLookupError) -> ApiError {
+    match error {
+        InvoiceLookupError::StripeClient { status } => {
+            let status = StatusCode::from_u16(status.as_u16()).unwrap_or(StatusCode::BAD_REQUEST);
+            match status {
+                StatusCode::NOT_FOUND => ApiError::NotFound("invoice not found"),
+                StatusCode::UNAUTHORIZED | StatusCode::FORBIDDEN => {
+                    ApiError::Forbidden("invoice access denied")
+                }
+                _ => ApiError::Client {
+                    status,
+                    code: "invoice-request-rejected",
+                    message: "invoice request rejected",
+                },
+            }
+        }
+        InvoiceLookupError::Internal(error) => ApiError::Internal(error.to_string()),
+    }
+}
+
 impl Api {
     pub fn new(query: Query, command: Command, billing: Billing) -> Self {
         let host = std::env::var("HOST").unwrap_or_else(|_| "127.0.0.1".to_string());
@@ -179,6 +209,9 @@ impl Api {
             return Err(ApiError::Unauthorized(anyhow!("missing u tag")));
         };
 
+        // Intentional session-style variant of NIP-98 for Caravel API auth.
+        // We validate signer identity plus host affinity, and do not bind to exact
+        // request URL/method or maintain replay state here.
         if !self.host.is_empty() && !got_u.contains(&self.host) {
             return Err(ApiError::Unauthorized(anyhow!(
                 "authorization host mismatch"
@@ -808,7 +841,7 @@ async fn get_invoice(
         .billing
         .get_invoice_with_tenant(&id)
         .await
-        .map_err(|e| ApiError::Internal(e.to_string()))?;
+        .map_err(map_invoice_lookup_error)?;
     state.api.require_admin_or_tenant(&auth, &tenant.pubkey)?;
 
     Ok(ok(StatusCode::OK, invoice))
@@ -825,7 +858,7 @@ async fn get_invoice_bolt11(
         .billing
         .get_invoice_with_tenant(&id)
         .await
-        .map_err(|e| ApiError::Internal(e.to_string()))?;
+        .map_err(map_invoice_lookup_error)?;
     state.api.require_admin_or_tenant(&auth, &tenant.pubkey)?;
 
     let status = invoice["status"].as_str().unwrap_or_default();

backend/src/billing.rs

@@ -18,6 +18,41 @@ const STRIPE_API: &str = "https://api.stripe.com/v1";
 const COINBASE_SPOT_API: &str = "https://api.coinbase.com/v2/prices";
 const WEBHOOK_TOLERANCE_SECS: i64 = 300;
 
+#[derive(Debug)]
+pub enum InvoiceLookupError {
+    StripeClient { status: reqwest::StatusCode },
+    Internal(anyhow::Error),
+}
+
+impl std::fmt::Display for InvoiceLookupError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::StripeClient { status } => {
+                write!(
+                    f,
+                    "stripe invoice lookup failed with status {}",
+                    status.as_u16()
+                )
+            }
+            Self::Internal(error) => write!(f, "{error}"),
+        }
+    }
+}
+
+impl std::error::Error for InvoiceLookupError {}
+
+impl From<anyhow::Error> for InvoiceLookupError {
+    fn from(value: anyhow::Error) -> Self {
+        Self::Internal(value)
+    }
+}
+
+impl From<reqwest::Error> for InvoiceLookupError {
+    fn from(value: reqwest::Error) -> Self {
+        Self::Internal(value.into())
+    }
+}
+
 #[derive(serde::Deserialize)]
 struct StripeEvent {
     #[serde(rename = "type")]
@@ -462,16 +497,18 @@ impl Billing {
     pub async fn get_invoice_with_tenant(
         &self,
         invoice_id: &str,
-    ) -> Result<(serde_json::Value, crate::models::Tenant)> {
+    ) -> std::result::Result<(serde_json::Value, crate::models::Tenant), InvoiceLookupError> {
         let invoice = self.stripe_get_invoice(invoice_id).await?;
         let customer_id = invoice["customer"]
             .as_str()
-            .ok_or_else(|| anyhow!("invoice missing customer"))?;
+            .ok_or_else(|| InvoiceLookupError::Internal(anyhow!("invoice missing customer")))?;
         let tenant = self
             .query
             .get_tenant_by_stripe_customer_id(customer_id)
             .await?
-            .ok_or_else(|| anyhow!("tenant not found for customer"))?;
+            .ok_or_else(|| {
+                InvoiceLookupError::Internal(anyhow!("tenant not found for customer"))
+            })?;
         Ok((invoice, tenant))
     }
 
@@ -515,7 +552,10 @@ impl Billing {
         Ok(body["data"].clone())
     }
 
-    pub async fn stripe_get_invoice(&self, invoice_id: &str) -> Result<serde_json::Value> {
+    pub async fn stripe_get_invoice(
+        &self,
+        invoice_id: &str,
+    ) -> std::result::Result<serde_json::Value, InvoiceLookupError> {
         let resp = self
             .http
             .get(format!("{STRIPE_API}/invoices/{invoice_id}"))
@@ -523,6 +563,12 @@ impl Billing {
             .send()
             .await?;
 
+        if resp.status().is_client_error() {
+            return Err(InvoiceLookupError::StripeClient {
+                status: resp.status(),
+            });
+        }
+
         let body: serde_json::Value = resp.error_for_status()?.json().await?;
         Ok(body)
     }

frontend/README.md

@@ -51,8 +51,11 @@ npm run preview
 
 ## Authentication
 
-- Tenant requests use NIP-98 tokens derived from the logged-in user
+- Tenant requests use an intentional session-style variant of NIP-98:
-- Admin routes require a pubkey listed in `PLATFORM_ADMIN_PUBKEYS` on the backend
+  - The client signs one kind `27235` event with `u = VITE_API_URL`.
+  - The resulting `Authorization` header is cached for about 10 minutes to avoid repeated signer prompts.
+  - The backend validates signer identity + host affinity rather than exact URL/method binding per request.
+- Admin routes require a pubkey listed in `ADMINS` on the backend.
 
 ## Routes
 

frontend/src/lib/api.ts

@@ -145,6 +145,8 @@ export async function makeAuth(): Promise<string | undefined> {
     kind: 27235,
     content: "",
     created_at: Math.floor(now / 1000),
+    // Intentional session-style auth: sign the API base URL once, then reuse
+    // the header briefly to avoid prompting the signer on every request.
     tags: [["u", API_URL]],
   })