Purchases.configure: log warning if attempting to use a static appUserID

Sources/Purchasing/Configuration.swift

@@ -113,11 +113,18 @@ import Foundation
          *
          * - Important: Set this property if you have your own user identifiers that you manage.
          */
+        @_disfavoredOverload
         @objc public func with(appUserID: String?) -> Builder {
             self.appUserID = appUserID
             return self
         }
 
+        // swiftlint:disable:next missing_docs
+        public func with(appUserID: StaticString) -> Configuration.Builder {
+            Logger.warn(Strings.identity.logging_in_with_static_string)
+            return self.with(appUserID: "\(appUserID)")
+        }
+
         /**
          * Set `observerMode`.
          * - Parameter observerMode: Set this to `true` if you have your own IAP implementation and want to use only

Tests/UnitTests/Purchasing/Purchases/PurchasesConfiguringTests.swift

@@ -158,6 +158,29 @@ class PurchasesConfiguringTests: BasePurchasesTests {
         expect(purchases.appUserID) == Self.appUserID
     }
 
+    func testStaticUserIdSringLogsMessage() {
+        let logger = TestLogHandler()
+
+        _ = Purchases.configure(
+            with: .init(withAPIKey: "")
+                .with(appUserID: "Static string")
+        )
+
+        logger.verifyMessageWasLogged(Strings.identity.logging_in_with_static_string)
+    }
+
+    func testUserIdSringDoesNotLogMessage() {
+        let appUserID = "user ID"
+        let logger = TestLogHandler()
+
+        _ = Purchases.configure(
+            with: .init(withAPIKey: "")
+                .with(appUserID: appUserID)
+        )
+
+        logger.verifyMessageWasNotLogged(Strings.identity.logging_in_with_static_string)
+    }
+
     @available(iOS 13.0, macOS 10.15, tvOS 13.0, watchOS 6.2, *)
     func testEntitlementVerificationModeDisabledDoesNotSetPublicKey() throws {
         try AvailabilityChecks.iOS13APIAvailableOrSkipTest()