[frontend] - Add Content Security Policy and Security Headers Audit

[dark-sarge]

Location: frontend/next.config.js

Description

No Content Security Policy (CSP) or other security headers are set on the Next.js frontend. Without a CSP, XSS attacks can steal JWT tokens or hijack the Paystack payment flow. A strict CSP and full security header audit must be implemented via Next.js's headers() config.

Acceptance Criteria

• next.config.js defines a headers() function that applies security headers to all routes: Content-Security-Policy, X-Frame-Options: DENY, X-Content-Type-Options: nosniff, Referrer-Policy: strict-origin-when-cross-origin, Permissions-Policy.
• The CSP allows: default-src 'self', Paystack JS from https://js.paystack.co, Next.js inline scripts via a nonce, and no unsafe-eval.
• The nonce-based CSP is implemented using Next.js middleware to generate a per-request nonce injected into the <script> tags and the CSP header simultaneously.
• https://securityheaders.com scores the deployed frontend at grade A or higher.
• HTTPS is enforced in production: the server sets Strict-Transport-Security: max-age=31536000; includeSubDomains.
• The CSP is tested against the Paystack inline checkout to ensure payment functionality is not broken by the policy.

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[iredis]

@iredis has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, I’ve reviewed the issue and understand the requirements. I’m confident I can deliver a clean solution that meets the acceptance criteria. Kindly assign it to me.

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[aymide1ee]

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[OMGO-Code]

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Hi Maintainer! I'd like to work on this issue. I'm confident I can complete it and submit a PR within 24 hours. Looking forward to contributing!

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[chinazapraise00-blip]

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Hello Maintainer, I’ve gone through the issue carefully and understand the requirements and expected outcome. I’m confident I can implement a clean, reliable solution that meets the acceptance criteria. I’d appreciate the opportunity to take ownership of this task and get started right away. Thank you!

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[Chris-P-web]

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[madaraUchiha1955]

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[Ofoedu-Ifeanyi]

@Ofoedu-Ifeanyi has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer I will really love to work on this project.i have all the needed skills to deliver this project if assigned

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