fix: Prevent error when switching accounts

src/identity/interaction/InteractionUtil.ts

@@ -86,4 +86,12 @@ export async function forgetWebId(provider: Provider, oidcInteraction: Interacti
     delete session.accountId;
     await session.persist();
   }
+
+  // If a client previously successfully completed an interaction a grant will have been created.
+  // If the same session gets reused to authenticate with a different WebID,
+  // we need to first delete the previous grant as the oidc-provider will try to reuse it.
+  if (oidcInteraction.grantId) {
+    const grant = await provider.Grant.find(oidcInteraction.grantId);
+    await grant?.destroy();
+  }
 }

test/unit/identity/interaction/InteractionUtil.test.ts

@@ -85,14 +85,31 @@ describe('InteractionUtil', (): void => {
             persist: jest.fn(),
           }),
         },
+        Grant: {
+          find: jest.fn().mockResolvedValue({
+            destroy: jest.fn(),
+          }),
+        },
       } as any;
     });
 
     it('removes the accountId from the session.', async(): Promise<void> => {
       await expect(forgetWebId(provider, oidcInteraction)).resolves.toBeUndefined();
+      expect(provider.Session.find).toHaveBeenCalledTimes(1);
+      expect(provider.Session.find).toHaveBeenLastCalledWith('cookie');
       const session = await (provider.Session.find as jest.Mock).mock.results[0].value;
       expect(session.accountId).toBeUndefined();
       expect(session.persist).toHaveBeenCalledTimes(1);
     });
+
+    it('deletes the grant if there is one associated to the session.', async(): Promise<void> => {
+      delete oidcInteraction.session;
+      oidcInteraction.grantId = 'grantId';
+      await expect(forgetWebId(provider, oidcInteraction)).resolves.toBeUndefined();
+      expect(provider.Grant.find).toHaveBeenCalledTimes(1);
+      expect(provider.Grant.find).toHaveBeenLastCalledWith('grantId');
+      const grant = await (provider.Grant.find as jest.Mock).mock.results[0].value;
+      expect(grant.destroy).toHaveBeenCalledTimes(1);
+    });
   });
 });