feat(crates-io): expose headers for ResponseError::Api

In response to RFC 3231 [^1], our registry client need to return headers
to caller, so that the caller (cargo binary) can continue parsing
challenge headers.

[^1]: https://rust-lang.github.io/rfcs/3231-cargo-asymmetric-tokens.html#the-authentication-process

Cargo.toml

@@ -27,7 +27,7 @@ cargo-util = { version = "0.2.5", path = "crates/cargo-util" }
 cargo_metadata = "0.14.0"
 clap = "4.2.0"
 core-foundation = { version = "0.9.0", features = ["mac_os_10_7_support"] }
-crates-io = { version = "0.37.0", path = "crates/crates-io" }
+crates-io = { version = "0.38.0", path = "crates/crates-io" }
 criterion = { version = "0.5.1", features = ["html_reports"] }
 curl = "0.4.44"
 curl-sys = "0.4.63"

crates/crates-io/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "crates-io"
-version = "0.37.0"
+version = "0.38.0"
 edition.workspace = true
 license.workspace = true
 repository = "https://github.com/rust-lang/cargo"

crates/crates-io/lib.rs

@@ -130,6 +130,7 @@ pub enum ResponseError {
     Curl(curl::Error),
     Api {
         code: u32,
+        headers: Vec<String>,
         errors: Vec<String>,
     },
     Code {
@@ -155,7 +156,7 @@ impl fmt::Display for ResponseError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
             ResponseError::Curl(e) => write!(f, "{}", e),
-            ResponseError::Api { code, errors } => {
+            ResponseError::Api { code, errors, .. } => {
                 f.write_str("the remote server responded with an error")?;
                 if *code != 200 {
                     write!(f, " (status {} {})", code, reason(*code))?;
@@ -447,7 +448,7 @@ impl Registry {
 
         match (self.handle.response_code()?, errors) {
             (0, None) | (200, None) => Ok(body),
-            (code, Some(errors)) => Err(ResponseError::Api { code, errors }),
+        (code, Some(errors)) => Err(ResponseError::Api { code, headers, errors }),
             (code, None) => Err(ResponseError::Code {
                 code,
                 headers,