Function parse_cmp_message 

pub fn parse_cmp_message(der: &[u8]) -> Result<CmpRequest, KipukaError>

Parse a DER-encoded CMP PKIMessage into a CmpRequest.

RFC 9810 §5: PKIMessage is an ASN.1 SEQUENCE:

PKIMessage ::= SEQUENCE {
    header     PKIHeader,
    body       PKIBody,
    protection [0] PKIProtection OPTIONAL,
    extraCerts [1] SEQUENCE SIZE (1..MAX) OF CMPCertificate OPTIONAL
}

This function performs minimal structural validation and extracts the fields needed for request dispatch.

Errors

• KipukaError::BadRequest — malformed DER, unknown message type, missing required header fields.
• KipukaError::Internal — full ASN.1 parsing not yet implemented.