Private sparse registry false positive

[Sculas]

Describe the bug
I have a private Cargo sparse registry. I've added the registry in .cargo/config.toml, and then used it in my Cargo.toml file like this:

# .cargo/config.toml
[registries]
example-internal = { index = "sparse+https://example.com/example/crates/" }

# Cargo.toml
[dependencies]
mylib = { version = "1", registry = "example-internal" }
# ...

I have my sources setup like this:

[sources]
unknown-registry = "deny"
allow-registry = [
    "https://github.com/rust-lang/crates.io-index",
    "sparse+https://example.com/example/crates/",
]

However, when running cargo deny check, I get these errors:

error[source-not-allowed]: detected 'registry' source not explicitly allowed
    ┌─ example\Cargo.lock:257:9
    │
257 │ mylib 1.0.0 sparse+https://example.com/example/crates/
    │             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ source
    │
    = mylib v1.0.0
      └── (dev) example v0.1.0

warning[unmatched-source]: allowed source was not encountered
   ┌─ example\deny.toml:23:5
   │
23 │     "sparse+https://example.com/example/crates/",
   │     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no crate source matched these criteria

advisories ok, bans ok, licenses ok, sources FAILED

To Reproduce
The information provided above should be enough, but you'll need to find a sparse registry to reproduce it.

Expected behavior
It should pass without any problems because the sources have been set up correctly.

Device:

• OS: Windows 11 22H2
• Version: d37423a

[Jake-Shadle]

Try removing the sparse+ prefix.

[Sculas]

Try removing the sparse+ prefix.

That seems to fix it. Should I keep this issue open?
If this is a wontfix, I think at least it should be documented that the sparse+ prefix must be removed.

[Jake-Shadle]

I guess I need to, I just didn't think it would be an issue since the regular git registry doesn't have the registry+ prefix.