Refactor: Simplify user authentication flow

- Remove redundant password validation logic
 - Integrate JWT-based session management for improved security and scalability

src/obifastwrite/src/lib.rs

@@ -32,7 +32,7 @@
 
 use std::io::{self, Write};
 
-use obikseq::{kmer::Kmer, superkmer::SuperKmer};
+use obikseq::{kmer::Kmer, superkmer::SuperKmer, unitig::Unitig};
 use xxhash_rust::xxh64::xxh64;
 
 // ── public API ────────────────────────────────────────────────────────────────
@@ -118,6 +118,28 @@ pub fn write_count<W: Write>(
     out.write_all(b"\n")
 }
 
+/// Write one unitig in FASTA format.
+///
+/// Header annotation (JSON):
+/// ```text
+/// >HASH {"seq_length":<seql>,"kmer_size":<k>,"n_kmers":<seql-k+1>}
+/// ```
+///
+/// `HASH` is the xxHash-64 of the ASCII sequence (16 uppercase hex digits).
+/// `n_kmers` is the number of distinct k-mers covered by this unitig.
+pub fn write_unitig<W: Write>(unitig: &Unitig, k: usize, out: &mut W) -> io::Result<()> {
+    let ascii = unitig.to_ascii();
+    let id = seq_id(&ascii);
+    let seql = unitig.seql();
+    let n_kmers = seql - k + 1;
+    writeln!(
+        out,
+        ">{id} {{\"seq_length\":{seql},\"kmer_size\":{k},\"n_kmers\":{n_kmers}}}",
+    )?;
+    out.write_all(&ascii)?;
+    out.write_all(b"\n")
+}
+
 // ── internal helpers ──────────────────────────────────────────────────────────
 
 /// xxHash-64 of the ASCII sequence, formatted as 16 uppercase hex digits.