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diff --git a/crates/credential/cargo-credential/Cargo.toml b/crates/credential/cargo-credential/Cargo.toml
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+++ b/crates/credential/cargo-credential/Cargo.toml
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+[package]
+name = "cargo-credential"
+version = "0.2.0"
+edition = "2021"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/cargo"
+description = "A library to assist writing Cargo credential helpers."
+
+[dependencies]
diff --git a/crates/credential/cargo-credential/README.md b/crates/credential/cargo-credential/README.md
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+# cargo-credential
+
+This package is a library to assist writing a Cargo credential helper, which
+provides an interface to store tokens for authorizing access to a registry
+such as https://crates.io/.
+
+Documentation about credential processes may be found at
+https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#credential-process
+
+Example implementations may be found at
+https://github.com/rust-lang/cargo/tree/master/crates/credential
+
+## Usage
+
+Create a Cargo project with this as a dependency:
+
+```toml
+# Add this to your Cargo.toml:
+
+[dependencies]
+cargo-credential = "0.1"
+```
+
+And then include a `main.rs` binary which implements the `Credential` trait, and calls
+the `main` function which will call the appropriate method of the trait:
+
+```rust
+// src/main.rs
+
+use cargo_credential::{Credential, Error};
+
+struct MyCredential;
+
+impl Credential for MyCredential {
+    /// implement trait methods here...
+}
+
+fn main() {
+    cargo_credential::main(MyCredential);
+}
+```
diff --git a/crates/credential/cargo-credential/src/lib.rs b/crates/credential/cargo-credential/src/lib.rs
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+++ b/crates/credential/cargo-credential/src/lib.rs
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+//! Helper library for writing Cargo credential processes.
+//!
+//! A credential process should have a `struct` that implements the `Credential` trait.
+//! The `main` function should be called with an instance of that struct, such as:
+//!
+//! ```rust,ignore
+//! fn main() {
+//!     cargo_credential::main(MyCredential);
+//! }
+//! ```
+//!
+//! This will determine the action to perform (get/store/erase) by looking at
+//! the CLI arguments for the first argument that does not start with `-`. It
+//! will then call the corresponding method of the trait to perform the
+//! requested action.
+
+pub type Error = Box<dyn std::error::Error>;
+
+pub trait Credential {
+    /// Returns the name of this credential process.
+    fn name(&self) -> &'static str;
+
+    /// Retrieves a token for the given registry.
+    fn get(&self, index_url: &str) -> Result<String, Error>;
+
+    /// Stores the given token for the given registry.
+    fn store(&self, index_url: &str, token: &str, name: Option<&str>) -> Result<(), Error>;
+
+    /// Removes the token for the given registry.
+    ///
+    /// If the user is not logged in, this should print a message to stderr if
+    /// possible indicating that the user is not currently logged in, and
+    /// return `Ok`.
+    fn erase(&self, index_url: &str) -> Result<(), Error>;
+}
+
+/// Runs the credential interaction by processing the command-line and
+/// environment variables.
+pub fn main(credential: impl Credential) {
+    let name = credential.name();
+    if let Err(e) = doit(credential) {
+        eprintln!("{} error: {}", name, e);
+        std::process::exit(1);
+    }
+}
+
+fn env(name: &str) -> Result<String, Error> {
+    std::env::var(name).map_err(|_| format!("environment variable `{}` is not set", name).into())
+}
+
+fn doit(credential: impl Credential) -> Result<(), Error> {
+    let which = std::env::args()
+        .skip(1)
+        .skip_while(|arg| arg.starts_with('-'))
+        .next()
+        .ok_or_else(|| "first argument must be the {action}")?;
+    let index_url = env("CARGO_REGISTRY_INDEX_URL")?;
+    let name = std::env::var("CARGO_REGISTRY_NAME_OPT").ok();
+    let result = match which.as_ref() {
+        "get" => credential.get(&index_url).and_then(|token| {
+            println!("{}", token);
+            Ok(())
+        }),
+        "store" => {
+            read_token().and_then(|token| credential.store(&index_url, &token, name.as_deref()))
+        }
+        "erase" => credential.erase(&index_url),
+        _ => {
+            return Err(format!(
+                "unexpected command-line argument `{}`, expected get/store/erase",
+                which
+            )
+            .into())
+        }
+    };
+    result.map_err(|e| format!("failed to `{}` token: {}", which, e).into())
+}
+
+fn read_token() -> Result<String, Error> {
+    let mut buffer = String::new();
+    std::io::stdin().read_line(&mut buffer)?;
+    if buffer.ends_with('\n') {
+        buffer.pop();
+    }
+    Ok(buffer)
+}