Implements Simple Certificate Enrollment Protocol with single-endpoint
operation-based dispatch (GetCACaps, GetCACert, PKIOperation), PKCS#7
SignedData CSR extraction with fallback for raw/base64 CSR, challenge
password authentication via CSR attributes, and shared internal/pkcs7
package extracted from EST handler to eliminate code duplication.
24 new tests (11 service + 13 handler) plus 5 shared pkcs7 package tests.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
shankar0123