Senior Front-End Engineer - 6 month contract at Denu Recruit, London Area, £550–£700 per day

Contract Opportunity: Senior Front-End Engineer, Identity Integration

6 months | Outside IR35 | Hybrid, 2–3 days in London | £550–£700 per day (flexible)

I’m working with a fast-growing fintech scale-up that has just been acquired by a global leader in financial and accounting software. As part of the acquisition, they’re bringing their platform together with one of the world’s most widely used small business accounting products. They need experienced contractors to help deliver that integration.

The work centres on identity: connecting the two platforms so users can sign in and move between them securely and seamlessly. It’s a high-visibility project inside a newly combined business, with real technical ownership of the user-facing experience.

What you’ll be doing:

• Building the user-facing sign-in, sign-up and account-linking journeys between the two platforms
• Implementing client-side authentication flows, including redirects, session handling and secure token storage
• Working closely with backend engineers on APIs and auth integration patterns
• Making sure the experience is secure, accessible, performant and production-ready

What we’re looking for:

• Strong front-end engineering experience with TypeScript and a modern framework such as React (Vue, Angular or similar are also welcome)
• Experience integrating front-end applications with APIs and backend services
• A track record of delivering polished, user-focused features on integration-heavy projects
• Comfort working autonomously as a contractor and getting productive quickly

Nice to have:

• Hands-on experience implementing OAuth 2.0 and/or OpenID Connect (OIDC) flows in the browser (e.g. PKCE, SSO)
• Background in identity, login or account management experiences
• Fintech or accounting software experience