Use context.formData if available over request.formData() (#14)

* Use context.formData if available over request.formData()

* Add docs

README.md

@@ -75,3 +75,21 @@ export const action: ActionFunction = async ({ request, context }) => {
   });
 };
 ```
+
+## Passing a pre-read FormData object
+
+Because you may want to do validations or read valeus from the FormData before calling `authenticate`, the FormStrategy allows you to pass a FormData object as part of the optional context.
+
+```ts
+export const action: ActionFunction = async ({ request, context }) => {
+  let formData = await request.formData();
+  return await authenticator.authenticate("form", request, {
+    // use formData here
+    successRedirect: formData.get("redirectTo"),
+    failureRedirect: "/login",
+    context: { formData }, // pass pre-read formData here
+  });
+};
+```
+
+This way, you don't need to clone the request yourself.

src/index.ts

@@ -27,7 +27,7 @@ export class FormStrategy<User> extends Strategy<
     sessionStorage: SessionStorage,
     options: AuthenticateOptions
   ): Promise<User> {
-    let form = await request.formData();
+    let form = await this.readFormData(request, options);
 
     let user: User;
     try {
@@ -39,4 +39,12 @@ export class FormStrategy<User> extends Strategy<
 
     return this.success(user, request, sessionStorage, options);
   }
+
+  private async readFormData(request: Request, options: AuthenticateOptions) {
+    if (options.context?.formData instanceof FormData) {
+      return options.context.formData;
+    }
+
+    return await request.formData();
+  }
 }

test/index.test.ts

@@ -70,4 +70,44 @@ describe(FormStrategy, () => {
 
     expect(verify).toBeCalledWith({ form: body, context });
   });
+
+  test("should prefer context.formData over request.formData()", async () => {
+    let body = new FormData();
+    body.set("email", "[email protected]");
+
+    let request = new Request("", { body, method: "POST" });
+
+    let context = { formData: body };
+
+    let strategy = new FormStrategy<string>(async ({ form }) => {
+      return form.get("email") as string;
+    });
+
+    expect(
+      strategy.authenticate(request, sessionStorage, {
+        sessionKey: "user",
+        context,
+      })
+    ).resolves.toBe("[email protected]");
+  });
+
+  test("ignore context.formData if it's not an FormData object", async () => {
+    let body = new FormData();
+    body.set("email", "[email protected]");
+
+    let request = new Request("", { body, method: "POST" });
+
+    let context = { formData: { email: "[email protected]" } };
+
+    let strategy = new FormStrategy<string>(async ({ form }) => {
+      return form.get("email") as string;
+    });
+
+    expect(
+      strategy.authenticate(request, sessionStorage, {
+        sessionKey: "user",
+        context,
+      })
+    ).resolves.toBe("[email protected]");
+  });
 });