Amp: detect login redirects and fail fast

Extracted from #324 (thanks @JosephDoUrden).

Author: ratulsarna

Sources/CodexBarCore/Providers/Amp/AmpUsageFetcher.swift

@@ -261,6 +261,9 @@ public struct AmpUsageFetcher: Sendable {
             if httpResponse.statusCode == 401 || httpResponse.statusCode == 403 {
                 throw AmpUsageError.invalidCredentials
             }
+            if diagnostics.detectedLoginRedirect {
+                throw AmpUsageError.invalidCredentials
+            }
             throw AmpUsageError.networkError("HTTP \(httpResponse.statusCode)")
         }
 
@@ -277,6 +280,7 @@ public struct AmpUsageFetcher: Sendable {
         private let cookieHeader: String
         private let logger: ((String) -> Void)?
         var redirects: [String] = []
+        private(set) var detectedLoginRedirect = false
 
         init(cookieHeader: String, logger: ((String) -> Void)?) {
             self.cookieHeader = cookieHeader
@@ -293,6 +297,16 @@ public struct AmpUsageFetcher: Sendable {
             let from = response.url?.absoluteString ?? "unknown"
             let to = request.url?.absoluteString ?? "unknown"
             self.redirects.append("\(response.statusCode) \(from) -> \(to)")
+
+            if let toURL = request.url, AmpUsageFetcher.isLoginRedirect(toURL) {
+                if let logger {
+                    logger("[amp] Detected login redirect, aborting (invalid session)")
+                }
+                self.detectedLoginRedirect = true
+                completionHandler(nil)
+                return
+            }
+
             var updated = request
             if AmpUsageFetcher.shouldAttachCookie(to: request.url), !self.cookieHeader.isEmpty {
                 updated.setValue(self.cookieHeader, forHTTPHeaderField: "Cookie")
@@ -364,4 +378,25 @@ public struct AmpUsageFetcher: Sendable {
         if host == "ampcode.com" || host == "www.ampcode.com" { return true }
         return host.hasSuffix(".ampcode.com")
     }
+
+    static func isLoginRedirect(_ url: URL) -> Bool {
+        guard self.shouldAttachCookie(to: url) else { return false }
+
+        let path = url.path.lowercased()
+        let components = path.split(separator: "/").map(String.init)
+        if components.contains("login") { return true }
+        if components.contains("signin") { return true }
+        if components.contains("sign-in") { return true }
+
+        // Amp currently redirects to /auth/sign-in?returnTo=... when session is invalid. Keep this slightly broader
+        // than one exact path so we keep working if Amp changes auth routes.
+        if components.contains("auth") {
+            let query = url.query?.lowercased() ?? ""
+            if query.contains("returnto=") { return true }
+            if query.contains("redirect=") { return true }
+            if query.contains("redirectto=") { return true }
+        }
+
+        return false
+    }
 }

Tests/CodexBarTests/AmpUsageFetcherTests.swift

@@ -17,4 +17,31 @@ struct AmpUsageFetcherTests {
         #expect(!AmpUsageFetcher.shouldAttachCookie(to: URL(string: "https://ampcode.com.evil.com")))
         #expect(!AmpUsageFetcher.shouldAttachCookie(to: nil))
     }
+
+    @Test
+    func detectsLoginRedirects() throws {
+        let signIn = try #require(URL(string: "https://ampcode.com/auth/sign-in?returnTo=%2Fsettings"))
+        #expect(AmpUsageFetcher.isLoginRedirect(signIn))
+
+        let sso = try #require(URL(string: "https://ampcode.com/auth/sso?returnTo=%2Fsettings"))
+        #expect(AmpUsageFetcher.isLoginRedirect(sso))
+
+        let login = try #require(URL(string: "https://ampcode.com/login"))
+        #expect(AmpUsageFetcher.isLoginRedirect(login))
+
+        let signin = try #require(URL(string: "https://www.ampcode.com/signin"))
+        #expect(AmpUsageFetcher.isLoginRedirect(signin))
+    }
+
+    @Test
+    func ignoresNonLoginURLs() throws {
+        let settings = try #require(URL(string: "https://ampcode.com/settings"))
+        #expect(!AmpUsageFetcher.isLoginRedirect(settings))
+
+        let signOut = try #require(URL(string: "https://ampcode.com/auth/sign-out"))
+        #expect(!AmpUsageFetcher.isLoginRedirect(signOut))
+
+        let evil = try #require(URL(string: "https://ampcode.com.evil.com/auth/sign-in"))
+        #expect(!AmpUsageFetcher.isLoginRedirect(evil))
+    }
 }