Builds the flattened JWS sent as usdid_token.sensitive_string_value in
IGUSDIDRegistrationMutation.
Encoding quirks observed on real Instagram Android traffic:
The outer envelope is the flattened JSON JWS ({payload, signatures:[…]}), then
the whole envelope is itself base64url-encoded (a non-standard outer wrap).
The ECDSA signature is DER-encoded in its minimal form, NOT the
JWS-standard raw R||S concatenation (which would be exactly 64 bytes). Its
length varies by a few bytes with the leading zero bytes of r and s.
Builds the flattened JWS sent as
usdid_token.sensitive_string_valueinIGUSDIDRegistrationMutation.Encoding quirks observed on real Instagram Android traffic:
{payload, signatures:[…]}), then the whole envelope is itself base64url-encoded (a non-standard outer wrap).rands.