dkim: add comparitive benchmark against mail-auth

```
signing/sign Simple     time:   [1.2990 ms 1.3002 ms 1.3015 ms]
                        thrpt:  [2.3581 MiB/s 2.3603 MiB/s 2.3626 MiB/s]
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild

signing/sign Relaxed    time:   [1.2942 ms 1.2955 ms 1.2968 ms]
                        thrpt:  [2.3665 MiB/s 2.3689 MiB/s 2.3712 MiB/s]
Found 4 outliers among 100 measurements (4.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
  2 (2.00%) high severe

mail-auth signing/sign Simple
                        time:   [487.97 µs 488.22 µs 488.48 µs]
                        thrpt:  [6.2826 MiB/s 6.2860 MiB/s 6.2892 MiB/s]
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high severe

mail-auth signing/sign Relaxed
                        time:   [494.68 µs 495.68 µs 496.68 µs]
                        thrpt:  [6.1789 MiB/s 6.1913 MiB/s 6.2039 MiB/s]
```

Cargo.lock

@@ -665,6 +665,7 @@ dependencies = [
  "ed25519-dalek",
  "futures",
  "indexmap",
+ "mail-auth",
  "mailparse",
  "memchr",
  "nom",

crates/dkim/Cargo.toml

@@ -29,9 +29,10 @@ tracing = "0.1"
 trust-dns-resolver = "0.22"
 
 [dev-dependencies]
-tokio = { version = "1.25", features = ["macros"] }
-regex = "1"
 criterion = "0.3"
+mail-auth = "0.3"
+regex = "1"
+tokio = { version = "1.25", features = ["macros"] }
 
 [[bench]]
 name = "sign"

crates/dkim/benches/sign.rs

@@ -3,7 +3,6 @@ use cfdkim::{DkimPrivateKey, ParsedEmail, SignerBuilder};
 use chrono::TimeZone;
 use criterion::{black_box, criterion_group, criterion_main, Criterion, SamplingMode, Throughput};
 use rsa::pkcs1::DecodeRsaPrivateKey;
-use std::path::Path;
 
 pub fn criterion_benchmark(c: &mut Criterion) {
     let email_text = r#"Subject: subject
@@ -50,12 +49,11 @@ aliquet eu tortor nec hendrerit. Aliquam in arcu ac erat venenatis pretium at si
 ipsum dolor sit a.
         "#
     .replace("\n", "\r\n");
+    let email = ParsedEmail::parse_bytes(email_text.as_bytes()).unwrap();
 
     for canon in [Type::Simple, Type::Relaxed] {
-        let email = ParsedEmail::parse_bytes(email_text.as_bytes()).unwrap();
-
         let private_key =
-            rsa::RsaPrivateKey::read_pkcs1_pem_file(Path::new("./test/keys/2022.private")).unwrap();
+            rsa::RsaPrivateKey::read_pkcs1_pem_file("./test/keys/2022.private").unwrap();
         let time = chrono::Utc.with_ymd_and_hms(2021, 1, 1, 0, 0, 1).unwrap();
 
         let signer = SignerBuilder::new()
@@ -78,6 +76,31 @@ ipsum dolor sit a.
         });
         group.finish();
     }
+
+    {
+        use mail_auth::common::crypto::{RsaKey, Sha256};
+        use mail_auth::dkim::{Canonicalization, DkimSigner};
+
+        for canon in [Canonicalization::Simple, Canonicalization::Relaxed] {
+            let key_data = std::fs::read_to_string("./test/keys/2022.private").unwrap();
+            let key = RsaKey::<Sha256>::from_rsa_pem(&key_data).unwrap();
+
+            let signer = DkimSigner::from_key(key)
+                .domain("example.com")
+                .selector("s20")
+                .headers(["From", "Subject"])
+                .header_canonicalization(canon)
+                .body_canonicalization(canon);
+
+            let mut group = c.benchmark_group("mail-auth signing");
+            group.sampling_mode(SamplingMode::Flat);
+            group.throughput(Throughput::Bytes(email_text.len() as u64));
+            group.bench_function(&format!("sign {canon:?}"), |b| {
+                b.iter(|| signer.sign(black_box(email_text.as_bytes())).unwrap())
+            });
+            group.finish();
+        }
+    }
 }
 
 criterion_group!(benches, criterion_benchmark);