1 files changed, 90 insertions, 0 deletions
diff --git a/src/tools/cargo/credential/cargo-credential/examples/file-provider.rs b/src/tools/cargo/credential/cargo-credential/examples/file-provider.rs
new file mode 100644
index 000000000..d11958536
--- /dev/null
+++ b/src/tools/cargo/credential/cargo-credential/examples/file-provider.rs
@@ -0,0 +1,90 @@
+//! Example credential provider that stores credentials in a JSON file.
+//! This is not secure
+
+use cargo_credential::{
+    Action, CacheControl, Credential, CredentialResponse, RegistryInfo, Secret,
+};
+use std::{collections::HashMap, fs::File, io::ErrorKind};
+type Error = Box<dyn std::error::Error + Send + Sync + 'static>;
+
+struct FileCredential;
+
+impl Credential for FileCredential {
+    fn perform(
+        &self,
+        registry: &RegistryInfo,
+        action: &Action,
+        _args: &[&str],
+    ) -> Result<CredentialResponse, cargo_credential::Error> {
+        if registry.index_url != "https://github.com/rust-lang/crates.io-index" {
+            // Restrict this provider to only work for crates.io. Cargo will skip it and attempt
+            // another provider for any other registry.
+            //
+            // If a provider supports any registry, then this check should be omitted.
+            return Err(cargo_credential::Error::UrlNotSupported);
+        }
+
+        // `Error::Other` takes a boxed `std::error::Error` type that causes Cargo to show the error.
+        let mut creds = FileCredential::read().map_err(cargo_credential::Error::Other)?;
+
+        match action {
+            Action::Get(_) => {
+                // Cargo requested a token, look it up.
+                if let Some(token) = creds.get(registry.index_url) {
+                    Ok(CredentialResponse::Get {
+                        token: token.clone(),
+                        cache: CacheControl::Session,
+                        operation_independent: true,
+                    })
+                } else {
+                    // Credential providers should respond with `NotFound` when a credential can not be
+                    // found, allowing Cargo to attempt another provider.
+                    Err(cargo_credential::Error::NotFound)
+                }
+            }
+            Action::Login(login_options) => {
+                // The token for `cargo login` can come from the `login_options` parameter or i
+                // interactively reading from stdin.
+                //
+                // `cargo_credential::read_token` automatically handles this.
+                let token = cargo_credential::read_token(login_options, registry)?;
+                creds.insert(registry.index_url.to_string(), token);
+
+                FileCredential::write(&creds).map_err(cargo_credential::Error::Other)?;
+
+                // Credentials were successfully stored.
+                Ok(CredentialResponse::Login)
+            }
+            Action::Logout => {
+                if creds.remove(registry.index_url).is_none() {
+                    // If the user attempts to log out from a registry that has no credentials
+                    // stored, then NotFound is the appropriate error.
+                    Err(cargo_credential::Error::NotFound)
+                } else {
+                    // Credentials were successfully erased.
+                    Ok(CredentialResponse::Logout)
+                }
+            }
+            // If a credential provider doesn't support a given operation, it should respond with `OperationNotSupported`.
+            _ => Err(cargo_credential::Error::OperationNotSupported),
+        }
+    }
+}
+
+impl FileCredential {
+    fn read() -> Result<HashMap<String, Secret<String>>, Error> {
+        match File::open("cargo-credentials.json") {
+            Ok(f) => Ok(serde_json::from_reader(f)?),
+            Err(e) if e.kind() == ErrorKind::NotFound => Ok(HashMap::new()),
+            Err(e) => Err(e)?,
+        }
+    }
+    fn write(value: &HashMap<String, Secret<String>>) -> Result<(), Error> {
+        let file = File::create("cargo-credentials.json")?;
+        Ok(serde_json::to_writer_pretty(file, value)?)
+    }
+}
+
+fn main() {
+    cargo_credential::main(FileCredential);
+}