Constant AUTHORIZATION_TOKEN 

const AUTHORIZATION_TOKEN: u64 = 0x03;

AUTHORIZATION TOKEN, the Version Specific Parameter of Section 8.2.1.1.

The number is this draft’s own. Draft-12 assigns AUTHORIZATION TOKEN “Parameter Type 0x03”; draft-11 put it at 0x01, where this draft has the setup-side PATH parameter instead. Reading either draft’s number into the other would exempt the wrong type from the repeat rule below.