PKCE — Proof Key for Code Exchange

Enterno.io Editorial Team

What is PKCE

By Anatoly Oshmanovsky · Updated Apr 17, 2026

Key idea:

PKCE (Proof Key for Code Exchange, RFC 7636) — an OAuth 2.0 extension protecting the authorization code from theft in public clients (SPAs, mobile apps without secure storage). Client generates a random code_verifier → sends a hash (code_challenge) in the authorize URL → at token exchange sends the original verifier back. Without PKCE, an attacker who intercepts the code can mint an access_token.

Below: details, example, related terms, FAQ.

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Details

code_verifier: random 43-128-char string (unique per auth attempt)
code_challenge: base64url(sha256(code_verifier))
code_challenge_method: S256 (only supported)
Authorize URL: adds code_challenge + method
Token exchange: sends the code_verifier instead of client_secret

Example

code_verifier = base64url(random(32))   // "dBjftJeZ..."
code_challenge = base64url(sha256(code_verifier))
auth_url = authorize?client_id=X&code_challenge=CC&code_challenge_method=S256

Related Terms

HeadersCSP, HSTS, X-Frame-Options, etc.

SSL/TLSEncryption and certificate

ConfigurationServer settings and leaks

Grade A-FOverall security score

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Enter site URL

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What Does the Security Analysis Check?

The tool checks HTTP security headers, SSL/TLS configuration, server info leaks, and protection against common attacks (XSS, clickjacking, MIME sniffing). A grade fromA to F shows overall security level.

Header Analysis

Checking Content-Security-Policy, HSTS, X-Frame-Options, X-Content-Type-Options, Referrer-Policy, and more.

SSL Check

TLS version, certificate expiry, chain of trust, HSTS support.

Leak Detection

Finding exposed server versions, debug modes, open configs, and directories.

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Detailed report explaining each issue with specific steps to fix it.

Who uses this

Security teams

HTTP header audit

DevOps

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Developers

CSP & HSTS setup

Auditors

compliance checks

Common Mistakes

❌

Missing Content-Security-PolicyCSP is the primary XSS defense. Without it, script injection is much easier.

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Missing HSTS headerWithout HSTS, HTTPS-to-HTTP downgrade attacks are possible. Enable Strict-Transport-Security.

❌

Server header exposes versionServer: Apache/2.4.52 helps attackers find exploits. Hide the version.

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X-Frame-Options not setSite can be embedded in iframe for clickjacking. Set DENY or SAMEORIGIN.

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Missing X-Content-Type-OptionsWithout nosniff, browsers may misinterpret file types (MIME sniffing).

Best Practices

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Start with basic headersMinimum: HSTS, X-Frame-Options, X-Content-Type-Options, Referrer-Policy. Takes 5 minutes.

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Implement CSP graduallyStart with Content-Security-Policy-Report-Only, monitor violations, then enforce.

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Hide server headersRemove Server, X-Powered-By, X-AspNet-Version from responses.

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Configure Permissions-PolicyRestrict camera, microphone, geolocation access — only what is actually used.

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Check after every deploySecurity headers can be overwritten during server configuration updates.

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Security check history and HTTP security header monitoring.

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How-to

Glossary

Research

Alternatives

Frequently Asked Questions

Is PKCE needed for confidential clients (server-side)?

Recommended (OAuth 2.1 draft) but not required. For public clients (SPA, mobile) — mandatory.

Do all providers support it?

All major ones: Google, GitHub, Microsoft, Auth0, Okta, Keycloak. Yandex OAuth since 2022.

Plain vs S256 method?

S256 (SHA-256) only in production. Plain (verifier=challenge) is legacy and insecure.