floonet-strfry: add a NIP-98 header-minting example for the name authority

Operating a NIP-98-gated endpoint (register / unregister / quote) needs signed
kind-27235 Authorization headers, and there is no nak on the target hosts. This
example reuses the crate's existing nostr/base64/sha2 deps to mint a
"Nostr <base64-event>" header for curl/CI: generate a throwaway identity or
reuse one via NIP98_SK, sign over the method/path/body, print the header to
stdout. The u-tag is built from FLOONET_BASE_URL to match server verification.

name-authority/examples/nip98.rs

@@ -0,0 +1,67 @@
+//! Mint a NIP-98 `Authorization: Nostr <base64-event>` header for calling this
+//! authority's authenticated endpoints (register / unregister / quote) with a
+//! plain HTTP client like `curl`. Handy for operators and CI: no external
+//! nostr tooling required, since the crate already depends on `nostr`.
+//!
+//! Usage:
+//!   # generate a throwaway identity (prints its secret+pubkey to stderr)
+//!   cargo run --example nip98 -- GET /api/v1/name/alice
+//!
+//!   # reuse an identity and sign over a request body
+//!   FLOONET_BASE_URL=https://nm.floonet.dev NIP98_SK=<64-hex-secret> \
+//!     cargo run --example nip98 -- POST /api/v1/register '{"name":"alice","pubkey":"<hex>"}'
+//!
+//! The header value is printed to stdout (nothing else), so it can be captured
+//! straight into a curl invocation:
+//!
+//!   AUTH=$(NIP98_SK=$SK cargo run -q --example nip98 -- POST /api/v1/register "$BODY")
+//!   curl -H "Authorization: $AUTH" -d "$BODY" https://nm.floonet.dev/api/v1/register
+//!
+//! The `u` tag is built from FLOONET_BASE_URL (default https://nm.floonet.dev),
+//! which MUST equal the authority's configured base URL — that is what the
+//! server verifies the signature's `u` tag against.
+
+use base64::Engine;
+use nostr::{EventBuilder, JsonUtil, Keys, Kind, Tag, Timestamp};
+use sha2::{Digest, Sha256};
+
+fn main() {
+    let mut args = std::env::args().skip(1);
+    let method = args
+        .next()
+        .expect("usage: nip98 <METHOD> <PATH> [BODY]  (e.g. POST /api/v1/register '{...}')");
+    let path = args
+        .next()
+        .expect("usage: nip98 <METHOD> <PATH> [BODY]  (e.g. POST /api/v1/register '{...}')");
+    let body = args.next().unwrap_or_default();
+
+    let base_url =
+        std::env::var("FLOONET_BASE_URL").unwrap_or_else(|_| "https://nm.floonet.dev".to_string());
+
+    let keys = match std::env::var("NIP98_SK") {
+        Ok(sk) if !sk.trim().is_empty() => Keys::parse(sk.trim()).expect("invalid NIP98_SK"),
+        _ => {
+            let k = Keys::generate();
+            eprintln!("generated secret (hex): {}", k.secret_key().to_secret_hex());
+            k
+        }
+    };
+    eprintln!("pubkey (hex): {}", keys.public_key().to_hex());
+
+    let url = format!("{base_url}{path}");
+    let mut tags = vec![
+        Tag::parse(["u", &url]).unwrap(),
+        Tag::parse(["method", &method]).unwrap(),
+    ];
+    if !body.is_empty() {
+        let payload = hex::encode(Sha256::digest(body.as_bytes()));
+        tags.push(Tag::parse(["payload", &payload]).unwrap());
+    }
+    let event = EventBuilder::new(Kind::HttpAuth, "")
+        .tags(tags)
+        .custom_created_at(Timestamp::now())
+        .sign_with_keys(&keys)
+        .expect("sign NIP-98 event");
+    let b64 = base64::engine::general_purpose::STANDARD.encode(event.as_json());
+    println!("Nostr {b64}");
+}