Error on invalid token for registry auth

When using registry operations with authentication there will be now an
error if the given token is not valid.
This is a technically a breaking change because a registry might give
some tokens which will be denied by these new checks.
In practice these tokens cause issues with HTTP so no registry should
generate them.

crates/crates-io/lib.rs

@@ -394,6 +394,7 @@ impl Registry {
                 Some(s) => s,
                 None => bail!("no upload token found, please run `cargo login`"),
             };
+            check_token(token)?;
             headers.append(&format!("Authorization: {}", token))?;
         }
         self.handle.http_headers(headers)?;
@@ -510,3 +511,23 @@ pub fn is_url_crates_io(url: &str) -> bool {
         .map(|u| u.host_str() == Some("crates.io"))
         .unwrap_or(false)
 }
+
+/// Checks if a token is valid or malformed.
+///
+/// This check is necessary to prevent sending tokens which create an invalid HTTP request.
+/// It would be easier to check just for alphanumeric tokens, but we can't be sure that all
+/// registries only create tokens in that format so that is as less restricted as possible.
+pub fn check_token(token: &str) -> Result<()> {
+    let is_valid = token.bytes().all(|b| {
+        b >= 32 // undefined in ISO-8859-1, in ASCII/ UTF-8 not-printable character
+        && b < 128 // utf-8: the first bit signals a multi-byte character
+        && b != 127 // 127 is a control character in ascii and not in ISO 8859-1
+        || b == b't' // tab is also allowed (even when < 32)
+    });
+
+    if is_valid {
+        Ok(())
+    } else {
+        Err(anyhow::anyhow!("invalid token."))
+    }
+}

src/cargo/ops/registry.rs

@@ -901,6 +901,7 @@ pub fn registry_login(
             if tok.is_empty() {
                 bail!("please provide a non-empty token");
             }
+            crates_io::check_token(tok.as_ref().expose())?;
         }
     }
     if &reg_cfg == &new_token {

tests/testsuite/login.rs

@@ -126,6 +126,38 @@ fn empty_login_token() {
         .run();
 }
 
+#[cargo_test]
+fn invalid_login_token() {
+    let registry = RegistryBuilder::new()
+        .no_configure_registry()
+        .no_configure_token()
+        .build();
+    setup_new_credentials();
+
+    let check_ = |stdin: &str, stderr: &str| {
+        cargo_process("login")
+            .replace_crates_io(registry.index_url())
+            .with_stdout("please paste the token found on [..]/me below")
+            .with_stdin(stdin)
+            .with_stderr(stderr)
+            .with_status(101)
+            .run();
+    };
+    let check = |stdin: &str| {
+        check_(stdin, "[ERROR] invalid token.");
+    };
+    // first check updates index so it must be handled differently
+    check_(
+        "😄",
+        "\
+[UPDATING] crates.io index
+[ERROR] invalid token.",
+    );
+    check("\u{0016}");
+    check("\u{0000}");
+    check("你好");
+}
+
 #[cargo_test]
 fn bad_asymmetric_token_args() {
     // These cases are kept brief as the implementation is covered by clap, so this is only smoke testing that we have clap configured correctly.