Add a uv auth helper --protocol bazel command

crates/uv-cli/src/lib.rs

@@ -4934,6 +4934,14 @@ pub enum AuthCommand {
     /// Credentials are only stored in this directory when the plaintext backend is used, as
     /// opposed to the native backend, which uses the system keyring.
     Dir(AuthDirArgs),
+    /// Act as a credential helper for external tools.
+    ///
+    /// Implements the Bazel credential helper protocol to provide credentials
+    /// to external tools via JSON over stdin/stdout.
+    ///
+    /// This command is typically invoked by external tools.
+    #[command(hide = true)]
+    Helper(AuthHelperArgs),
 }
 
 #[derive(Args)]
@@ -6215,6 +6223,30 @@ pub struct AuthDirArgs {
     pub service: Option<Service>,
 }
 
+#[derive(Args)]
+pub struct AuthHelperArgs {
+    #[command(subcommand)]
+    pub command: AuthHelperCommand,
+
+    /// The credential helper protocol to use
+    #[arg(long, value_enum, required = true)]
+    pub protocol: AuthHelperProtocol,
+}
+
+/// Credential helper protocols supported by uv
+#[derive(Debug, Copy, Clone, PartialEq, Eq, clap::ValueEnum)]
+pub enum AuthHelperProtocol {
+    /// Bazel credential helper protocol as described in [the
+    /// spec](https://github.com/bazelbuild/proposals/blob/main/designs/2022-06-07-bazel-credential-helpers.md)
+    Bazel,
+}
+
+#[derive(Subcommand)]
+pub enum AuthHelperCommand {
+    /// Retrieve credentials for a URI
+    Get,
+}
+
 #[derive(Args)]
 pub struct GenerateShellCompletionArgs {
     /// The shell to generate the completion script for

crates/uv-preview/src/lib.rs

@@ -26,6 +26,7 @@ bitflags::bitflags! {
         const WORKSPACE_DIR = 1 << 14;
         const WORKSPACE_LIST = 1 << 15;
         const SBOM_EXPORT = 1 << 16;
+        const AUTH_HELPER = 1 << 17;
     }
 }
 
@@ -52,6 +53,7 @@ impl PreviewFeatures {
             Self::WORKSPACE_DIR => "workspace-dir",
             Self::WORKSPACE_LIST => "workspace-list",
             Self::SBOM_EXPORT => "sbom-export",
+            Self::AUTH_HELPER => "auth-helper",
             _ => panic!("`flag_as_str` can only be used for exactly one feature flag"),
         }
     }
@@ -106,6 +108,7 @@ impl FromStr for PreviewFeatures {
                 "workspace-dir" => Self::WORKSPACE_DIR,
                 "workspace-list" => Self::WORKSPACE_LIST,
                 "sbom-export" => Self::SBOM_EXPORT,
+                "auth-helper" => Self::AUTH_HELPER,
                 _ => {
                     warn_user_once!("Unknown preview feature: `{part}`");
                     continue;

crates/uv/src/commands/auth/helper.rs

@@ -0,0 +1,151 @@
+use std::collections::HashMap;
+use std::fmt::Write;
+use std::io::Read;
+
+use anyhow::{Context, Result, bail};
+use serde::{Deserialize, Serialize};
+use tracing::debug;
+
+use uv_auth::{AuthBackend, Credentials, PyxTokenStore};
+use uv_client::BaseClientBuilder;
+use uv_preview::{Preview, PreviewFeatures};
+use uv_redacted::DisplaySafeUrl;
+use uv_warnings::warn_user;
+
+use crate::{commands::ExitStatus, printer::Printer, settings::NetworkSettings};
+
+/// Request format for the Bazel credential helper protocol.
+#[derive(Debug, Deserialize)]
+struct BazelCredentialRequest {
+    uri: DisplaySafeUrl,
+}
+
+impl BazelCredentialRequest {
+    fn from_str(s: &str) -> Result<Self> {
+        serde_json::from_str(s).context("Failed to parse credential request as JSON")
+    }
+
+    fn from_stdin() -> Result<Self> {
+        let mut buffer = String::new();
+        std::io::stdin()
+            .read_to_string(&mut buffer)
+            .context("Failed to read from stdin")?;
+
+        Self::from_str(&buffer)
+    }
+}
+
+/// Response format for the Bazel credential helper protocol.
+#[derive(Debug, Serialize, Default)]
+struct BazelCredentialResponse {
+    headers: HashMap<String, Vec<String>>,
+}
+
+impl TryFrom<Credentials> for BazelCredentialResponse {
+    fn try_from(creds: Credentials) -> Result<Self> {
+        let header_str = creds
+            .to_header_value()
+            .to_str()
+            // TODO: this is infallible in practice
+            .context("Failed to convert header value to string")?
+            .to_owned();
+
+        Ok(Self {
+            headers: HashMap::from([("Authorization".to_owned(), vec![header_str])]),
+        })
+    }
+
+    type Error = anyhow::Error;
+}
+
+async fn credentials_for_url(
+    url: &DisplaySafeUrl,
+    preview: Preview,
+    network_settings: &NetworkSettings,
+) -> Result<Option<Credentials>> {
+    let pyx_store = PyxTokenStore::from_settings()?;
+
+    // Use only the username from the URL, if present - discarding the password
+    let url_credentials = Credentials::from_url(url);
+    let username = url_credentials.as_ref().and_then(|c| c.username());
+    if url_credentials
+        .as_ref()
+        .map(|c| c.password().is_some())
+        .unwrap_or(false)
+    {
+        debug!("URL '{url}' contain a password; ignoring");
+    }
+
+    if pyx_store.is_known_domain(url) {
+        if username.is_some() {
+            bail!(
+                "Cannot specify a username for URLs under {}",
+                url.host()
+                    .map(|host| host.to_string())
+                    .unwrap_or(url.to_string())
+            );
+        }
+        let client = BaseClientBuilder::new(
+            network_settings.connectivity,
+            network_settings.native_tls,
+            network_settings.allow_insecure_host.clone(),
+            preview,
+            network_settings.timeout,
+            network_settings.retries,
+        )
+        .auth_integration(uv_client::AuthIntegration::NoAuthMiddleware)
+        .build();
+        let token = pyx_store
+            .access_token(client.for_host(pyx_store.api()).raw_client(), 0)
+            .await
+            .context("Authentication failure")?
+            .context("No access token found")?;
+        return Ok(Some(Credentials::bearer(token.into_bytes())));
+    }
+    let backend = AuthBackend::from_settings(preview).await?;
+    let credentials = match &backend {
+        AuthBackend::System(provider) => provider.fetch(url, username).await,
+        AuthBackend::TextStore(store, _lock) => store.get_credentials(url, username).cloned(),
+    };
+    Ok(credentials)
+}
+
+/// Implement the Bazel credential helper protocol.
+///
+/// Reads a JSON request from stdin containing a URI, looks up credentials
+/// for that URI using uv's authentication backends, and writes a JSON response
+/// to stdout containing HTTP headers (if credentials are found).
+///
+/// Protocol specification TLDR:
+/// - Input (stdin): `{"uri": "https://example.com/path"}`
+/// - Output (stdout): `{"headers": {"Authorization": ["Basic ..."]}}` or `{"headers": {}}`
+/// - Errors: Written to stderr with non-zero exit code
+///
+/// Full spec is [available here](https://github.com/bazelbuild/proposals/blob/main/designs/2022-06-07-bazel-credential-helpers.md)
+pub(crate) async fn helper(
+    preview: Preview,
+    network_settings: &NetworkSettings,
+    printer: Printer,
+) -> Result<ExitStatus> {
+    if !preview.is_enabled(PreviewFeatures::AUTH_HELPER) {
+        warn_user!(
+            "The `uv auth helper` command is experimental and may change without warning. Pass `--preview-features {}` to disable this warning",
+            PreviewFeatures::AUTH_HELPER
+        );
+    }
+
+    let request = BazelCredentialRequest::from_stdin()?;
+
+    // TODO: make this logic generic over the protocol by providing `request.uri` from a
+    // trait - that should help with adding new protocols
+    let credentials = credentials_for_url(&request.uri, preview, network_settings).await?;
+
+    let response = serde_json::to_string(
+        &credentials
+            .map(BazelCredentialResponse::try_from)
+            .unwrap_or_else(|| Ok(BazelCredentialResponse::default()))?,
+    )
+    .context("Failed to serialize response as JSON")?;
+    writeln!(printer.stdout_important(), "{response}")?;
+    Ok(ExitStatus::Success)
+}

crates/uv/src/commands/auth/mod.rs

@@ -1,4 +1,5 @@
 pub(crate) mod dir;
+pub(crate) mod helper;
 pub(crate) mod login;
 pub(crate) mod logout;
 pub(crate) mod token;

crates/uv/src/commands/mod.rs

@@ -10,6 +10,7 @@ use owo_colors::OwoColorize;
 use tracing::debug;
 
 pub(crate) use auth::dir::dir as auth_dir;
+pub(crate) use auth::helper::helper as auth_helper;
 pub(crate) use auth::login::login as auth_login;
 pub(crate) use auth::logout::logout as auth_logout;
 pub(crate) use auth::token::token as auth_token;

crates/uv/src/lib.rs

@@ -26,10 +26,10 @@ use uv_cache_info::Timestamp;
 #[cfg(feature = "self-update")]
 use uv_cli::SelfUpdateArgs;
 use uv_cli::{
-    AuthCommand, AuthNamespace, BuildBackendCommand, CacheCommand, CacheNamespace, Cli, Commands,
-    PipCommand, PipNamespace, ProjectCommand, PythonCommand, PythonNamespace, SelfCommand,
-    SelfNamespace, ToolCommand, ToolNamespace, TopLevelArgs, WorkspaceCommand, WorkspaceNamespace,
-    compat::CompatArgs,
+    AuthCommand, AuthHelperCommand, AuthNamespace, BuildBackendCommand, CacheCommand,
+    CacheNamespace, Cli, Commands, PipCommand, PipNamespace, ProjectCommand, PythonCommand,
+    PythonNamespace, SelfCommand, SelfNamespace, ToolCommand, ToolNamespace, TopLevelArgs,
+    WorkspaceCommand, WorkspaceNamespace, compat::CompatArgs,
 };
 use uv_client::BaseClientBuilder;
 use uv_configuration::min_stack_size;
@@ -542,6 +542,22 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
             commands::auth_dir(args.service.as_ref(), printer)?;
             Ok(ExitStatus::Success)
         }
+        Commands::Auth(AuthNamespace {
+            command: AuthCommand::Helper(args),
+        }) => {
+            use uv_cli::AuthHelperProtocol;
+
+            // Validate protocol (currently only Bazel is supported)
+            match args.protocol {
+                AuthHelperProtocol::Bazel => {}
+            }
+
+            match args.command {
+                AuthHelperCommand::Get => {
+                    commands::auth_helper(globals.preview, &globals.network_settings, printer).await
+                }
+            }
+        }
         Commands::Help(args) => commands::help(
             args.command.unwrap_or_default().as_slice(),
             printer,