chore: check continurUrl is present before continuing

Author: russellwheatley

FirebaseSwiftUI/FirebaseAuthSwiftUI/Sources/AuthServiceError.swift

@@ -13,7 +13,7 @@ public struct AccountMergeConflictContext: LocalizedError {
 }
 
 public enum AuthServiceError: LocalizedError {
-  case invalidEmailLink
+  case invalidEmailLink(String)
   case notConfiguredProvider(String)
   case clientIdNotFound(String)
   case notConfiguredActionCodeSettings(String)
@@ -24,8 +24,8 @@ public enum AuthServiceError: LocalizedError {
 
   public var errorDescription: String? {
     switch self {
-    case .invalidEmailLink:
-      return "Invalid sign in link. Most likely, the link you used has expired. Try signing in again."
+    case let .invalidEmailLink(description):
+      return description
     case let .notConfiguredProvider(description):
       return description
     case let .clientIdNotFound(description):

FirebaseSwiftUI/FirebaseAuthSwiftUI/Sources/Services/AuthService.swift

@@ -302,12 +302,20 @@ public extension AuthService {
   func handleSignInLink(url url: URL) async throws {
     do {
       guard let email = emailLink else {
-        throw AuthServiceError.invalidEmailLink
+        throw AuthServiceError.invalidEmailLink("email address is missing from local storage")
       }
       let link = url.absoluteString
+      guard let continueUrl = CommonUtils.getQueryParamValue(from: link, paramName: "continueUrl")
+      else {
+        throw AuthServiceError
+          .invalidEmailLink("`continueUrl` parameter is missing from the email link URL")
+      }
 
       if auth.isSignIn(withEmailLink: link) {
-        let anonymousUserID = CommonUtils.getAnonymousUserIdFromUrl(from: link)
+        let anonymousUserID = CommonUtils.getQueryParamValue(
+          from: continueUrl,
+          paramName: "ui_auid"
+        )
         if shouldHandleAnonymousUpgrade, anonymousUserID == currentUser?.uid {
           let credential = EmailAuthProvider.credential(withEmail: email, link: link)
           try await handleAutoUpgradeAnonymousUser(credentials: credential)

FirebaseSwiftUI/FirebaseAuthSwiftUI/Sources/Utils/CommonUtils.swift

@@ -54,9 +54,4 @@ public class CommonUtils {
 
     return urlComponents.queryItems?.first(where: { $0.name == paramName })?.value
   }
-
-  public static func getAnonymousUserIdFromUrl(from urlString: String) -> String? {
-    getQueryParamValue(from: urlString, paramName: "continueUrl")
-      .flatMap { getQueryParamValue(from: $0, paramName: "ui_auid") }
-  }
 }