Expose method to take missing headers from RequiredError

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "http-signature-normalization"
 description = "An HTTP Signatures library that leaves the signing to you"
-version = "0.5.3"
+version = "0.5.4"
 authors = ["asonix <asonix@asonix.dog>"]
 license-file = "LICENSE"
 readme = "README.md"
@@ -16,7 +16,7 @@ members = [
     "http-signature-normalization-actix",
     "http-signature-normalization-http",
     "http-signature-normalization-reqwest",
-    "http-signature-normalization-warp",
+    # "http-signature-normalization-warp",
 ]
 
 [dependencies]

src/lib.rs

@@ -99,6 +99,18 @@ pub enum PrepareVerifyError {
 /// Failed to build a signing string due to missing required headers
 pub struct RequiredError(HashSet<String>);
 
+impl RequiredError {
+    /// Retrieve the missing headers from the error
+    pub fn headers(&self) -> &HashSet<String> {
+        &self.0
+    }
+
+    /// Take the headers from the error
+    pub fn take_headers(&mut self) -> HashSet<String> {
+        std::mem::take(&mut self.0)
+    }
+}
+
 impl Config {
     /// Create a new Config with a default expiration of 10 seconds
     pub fn new() -> Self {