index.ts

// path: resolvers/mutation/login/index.ts

import { WrongCredentialsError } from "./errors/WrongCredentialsError";

interface LoginInput {
  username: string;
  password: string;
}

const login = await (parent, args: LoginInput, context: Context, info) {
    const user = await context.db.query.user({where: {username: args.username}});

    const areCredentialsValid = checkCredentials(user, args.password);

    if (!areCredentialsValid) {
        throw new WrongCredentialsError();
    }
};