[Docs] Missing GMP/BCMath requirement warning for web-token/jwt-library

[guillaumebeausse-dev]

The Symfony documentation recommends installing web-token/jwt-library without warning that the GMP or BCMath PHP extension is required for acceptable performance.

composer require web-token/jwt-library symfony/cache

Without these extensions, the library falls back to brick/math's pure PHP implementation for big integer operations, resulting in extremely slow RSA signature verification.

Benchmark results (RSA-256, 2048-bit key)

PHP Extension	JWT verification time	Relative performance
None (pure PHP)	~1,568 ms	780x slower
BCMath	~10 ms	5x slower
GMP	~2 ms	baseline

Impact

• API response times of 1.5+ seconds per authenticated request
• Timeouts on high-traffic applications
• Difficult to diagnose (no error, just slow performance)

Root cause

1. web-token/jwt-library depends on brick/math
2. brick/math silently falls back to pure PHP when GMP/BCMath are unavailable
3. The [web-token documentation](https://web-token.spomky-labs.com/introduction/pre-requisite) mentions this requirement, but the Symfony docs do not

Suggested fix

Add a note to the documentation recommending GMP installation:

> **Performance Warning:** For production use, ensure the GMP PHP extension is installed. 
> Without it, JWT verification can be up to 780x slower.

References

• [web-token prerequisites](https://web-token.spomky-labs.com/introduction/pre-requisite)
• [brick/math repository](https://github.com/brick/math)
• [brick/math#56 - Related performance discussion](Fatal error: Maximum execution time of 30 seconds exceeded brick/math#56)