Credential provider protocol fails with strings containing escaped characters

Problem

The structures defined in the credential provider protocol use borrowed string (&'a str) types that can only be deserialized if they don't contain any characters that need to be escaped by JSON. If escaping is required then the deserialization fails with:

invalid type: string "test\ning", expected a borrowed string

This can occur if, for example, the user attempts to use a " in a registry auth token. This is not a bug in the JSON protocol itself.

Steps

1. Set up a credential provider
2. Run cargo login
3. Use a token that contains a "

Possible Solution(s)

1. Switch to using Cow<'a, str> in the credential struct definitions.
2. Switch to using String in the struct definitions.

Any solution seems to require a breaking change to the credential struct definitions.

Notes

No response

Version

cargo 1.78.0-nightly (fc1d58fd0 2024-02-09)
release: 1.78.0-nightly
commit-hash: fc1d58fd0531a57a6b942a14cdcdbcb82ece16f3
commit-date: 2024-02-09
host: x86_64-pc-windows-msvc
libgit2: 1.7.2 (sys:0.18.2 vendored)
libcurl: 8.6.0-DEV (sys:0.4.71+curl-8.6.0 vendored ssl:Schannel)
os: Windows 10.0.26085 (Windows 11 Enterprise) [64-bit]

Start by locating the credential provider protocol definitions and the deserialization path exercised by cargo login. Reproduce the failure with a token containing an escaped character, then determine whether the protocol types should use Cow<'a, str> or String and add coverage for escaped credentials.