Add accept-invite function (#1180)

## Description

The endpoint is still behind a feature flag, but this makes it
available.

## Documentation

Does this require changes to the WorkOS Docs? E.g. the [API
Reference](https://workos.com/docs/reference) or code snippets need
updates.

```
[x] Yes
```

If yes, link a related docs PR and add a docs maintainer as a reviewer.
Their approval is required.

workos/workos#32872

src/user-management/interfaces/invitation.interface.ts

@@ -8,6 +8,7 @@ export interface Invitation {
   expiresAt: string;
   organizationId: string | null;
   inviterUserId: string | null;
+  acceptedUserId: string | null;
   token: string;
   acceptInvitationUrl: string;
   createdAt: string;
@@ -24,6 +25,7 @@ export interface InvitationEvent {
   expiresAt: string;
   organizationId: string | null;
   inviterUserId: string | null;
+  acceptedUserId: string | null;
   createdAt: string;
   updatedAt: string;
 }
@@ -38,6 +40,7 @@ export interface InvitationResponse {
   expires_at: string;
   organization_id: string | null;
   inviter_user_id: string | null;
+  accepted_user_id: string | null;
   token: string;
   accept_invitation_url: string;
   created_at: string;
@@ -54,6 +57,7 @@ export interface InvitationEventResponse {
   expires_at: string;
   organization_id: string | null;
   inviter_user_id: string | null;
+  accepted_user_id: string | null;
   created_at: string;
   updated_at: string;
 }

src/user-management/serializers/invitation.serializer.ts

@@ -17,6 +17,7 @@ export const deserializeInvitation = (
   expiresAt: invitation.expires_at,
   organizationId: invitation.organization_id,
   inviterUserId: invitation.inviter_user_id,
+  acceptedUserId: invitation.accepted_user_id,
   token: invitation.token,
   acceptInvitationUrl: invitation.accept_invitation_url,
   createdAt: invitation.created_at,
@@ -35,6 +36,7 @@ export const deserializeInvitationEvent = (
   expiresAt: invitation.expires_at,
   organizationId: invitation.organization_id,
   inviterUserId: invitation.inviter_user_id,
+  acceptedUserId: invitation.accepted_user_id,
   createdAt: invitation.created_at,
   updatedAt: invitation.updated_at,
 });

src/user-management/user-management.spec.ts

@@ -1708,6 +1708,31 @@ describe('UserManagement', () => {
     });
   });
 
+  describe('acceptInvitation', () => {
+    it('sends an Accept Invitation request', async () => {
+      const invitationId = 'invitation_01H5JQDV7R7ATEYZDEG0W5PRYS';
+      fetchOnce({
+        ...invitationFixture,
+        state: 'accepted',
+        accepted_user_id: 'user_01HGK4K4PXNSG85RNNV0GXYP5W',
+      });
+
+      const response = await workos.userManagement.acceptInvitation(
+        invitationId,
+      );
+
+      expect(fetchURL()).toContain(
+        `/user_management/invitations/${invitationId}/accept`,
+      );
+      expect(response).toMatchObject({
+        object: 'invitation',
+        email: '[email protected]',
+        state: 'accepted',
+        acceptedUserId: 'user_01HGK4K4PXNSG85RNNV0GXYP5W',
+      });
+    });
+  });
+
   describe('revokeInvitation', () => {
     it('send a Revoke Invitation request', async () => {
       const invitationId = 'invitation_01H5JQDV7R7ATEYZDEG0W5PRYS';

src/user-management/user-management.ts

@@ -940,6 +940,15 @@ export class UserManagement {
     return deserializeInvitation(data);
   }
 
+  async acceptInvitation(invitationId: string): Promise<Invitation> {
+    const { data } = await this.workos.post<InvitationResponse, any>(
+      `/user_management/invitations/${invitationId}/accept`,
+      null,
+    );
+
+    return deserializeInvitation(data);
+  }
+
   async revokeInvitation(invitationId: string): Promise<Invitation> {
     const { data } = await this.workos.post<InvitationResponse, any>(
       `/user_management/invitations/${invitationId}/revoke`,