Function create_nip98_authorization 

pub fn create_nip98_authorization(
    identity: &LocalIdentity,
    method: &str,
    url: &str,
    payload: Option<&[u8]>,
    created_at: u64,
) -> Result<HttpAuthorizationPlan, SoftchatError>

Create an immutable, signed NIP-98 HTTP authorization plan.

Platform adapters execute the request and must create a fresh plan after any redirect. The Authorization header is deliberately not reusable on a different method or URL.

Errors

Returns SoftchatError::InvalidHttpAuthorization for invalid methods, URLs, payload bounds, or signing failures.