diff --git a/AltSign/Sources/ALTAppleAPI+Authentication.swift b/AltSign/Sources/ALTAppleAPI+Authentication.swift
index 2d3e50c2..34149216 100644
--- a/AltSign/Sources/ALTAppleAPI+Authentication.swift
+++ b/AltSign/Sources/ALTAppleAPI+Authentication.swift
@@ -446,11 +446,28 @@ private extension ALTAppleAPI
             request.httpBody = bodyData
             httpHeaders.forEach { request.addValue($0.value, forHTTPHeaderField: $0.key) }
             
-            let dataTask = self.session.dataTask(with: request) { (data, response, error) in
+            // Apple's edge serves at most two requests per connection and answers every request
+            // after that with a 503 HTML error page. Authenticating takes three requests (init,
+            // complete, apptokens), so the third one fails whenever they share a pooled connection.
+            // Give each request its own session, and therefore its own connection.
+            let configuration = URLSessionConfiguration.ephemeral
+            configuration.httpMaximumConnectionsPerHost = 1
+            let session = URLSession(configuration: configuration)
+            defer { session.finishTasksAndInvalidate() }
+            
+            let dataTask = session.dataTask(with: request) { (data, response, error) in
                 do
                 {
                     guard let data = data else { throw error ?? ALTAppleAPIError.unknown() }
                     
+                    // Surface server errors directly; their HTML bodies are not property lists, and
+                    // parsing them yields a misleading "data couldn't be read" error instead.
+                    if let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode >= 500
+                    {
+                        let message = String(format: NSLocalizedString("Apple's authentication servers returned an error (HTTP %d). This is a problem on Apple's end, not with your Apple ID or password.", comment: ""), httpResponse.statusCode)
+                        throw NSError(domain: ALTUnderlyingAppleAPIErrorDomain, code: httpResponse.statusCode, userInfo: [NSLocalizedDescriptionKey: message])
+                    }
+                    
                     guard let responseDictionary = try PropertyListSerialization.propertyList(from: data, format: nil) as? [String: Any],
                           let dictionary = responseDictionary["Response"] as? [String: Any],
                           let status = dictionary["Status"] as? [String: Any]