hive-forge: stop embedding the forge token in clone URLs

docs/tools/forge.md

@@ -144,7 +144,7 @@ lets a read-only user open a PR by pushing the current `HEAD` to the
 magic ref `refs/for/<base>/<topic>`. Two verbs cover the workflow:
 
 ```
-hive-forge -r internal/knowledge clone          # clone with token auto-injected
+hive-forge -r internal/knowledge clone          # clone, auth handled for you
 cd knowledge
 # add / edit / delete any files, then commit normally
 git add -A && git commit -m "add foo runbook"
@@ -155,9 +155,13 @@ hive-forge -r internal/knowledge pr-create --agit \
 ```
 
 `clone` derives the dest dir from the repo basename (override with a
-positional arg); `--branch` / `--depth` are passed through. The token
-is injected into the clone's `origin` remote so `pr-create --agit`
-(default remote `origin`) can push without re-auth.
+positional arg); `--branch` / `--depth` are passed through. The clone
+URL and the `origin` remote it leaves behind carry no credentials —
+`clone` instead configures `origin`'s `credential.helper` to invoke
+`hive-forge credential-helper` (a hidden verb, not meant to be run by
+hand), which git calls fresh on every fetch/push. That's what lets
+`pr-create --agit` (default remote `origin`) push without re-auth,
+without a durable token sitting in the checkout's `.git/config`.
 
 `pr-create --agit` prints the PR URL. Re-running with the same
 `--topic` force-updates the existing open PR (the AGit ref is

hive-forge/src/client.rs

@@ -31,10 +31,12 @@ pub struct Client {
     /// header the typed client sends.
     web: HttpClient,
     base: String,
-    /// Per-agent forge token. Kept so verbs that shell out to `git`
-    /// (e.g. `clone`) can assemble an authenticated push URL without
-    /// re-reading the token file.
-    token: String,
+    /// The `-f/--forge` label this client resolved against, `None` for
+    /// the default internal forge. `clone` bakes this back into the
+    /// `credential.helper` command it configures, so a later `git push`/
+    /// `git fetch` in that checkout re-resolves the *same* forge account
+    /// rather than silently falling back to the internal one.
+    forge_label: Option<String>,
     /// Default repo used when a verb doesn't carry an explicit
     /// `[repo]` override.
     pub default_repo: String,
@@ -98,7 +100,7 @@ impl Client {
             api,
             web,
             base,
-            token,
+            forge_label,
             default_repo,
             json_mode,
         })
@@ -111,21 +113,26 @@ impl Client {
         &self.api
     }
 
-    /// Assemble an authenticated git URL for `repo` (e.g.
-    /// `internal/knowledge`) by injecting the agent's forge user +
-    /// token into the base URL's authority: `http://<user>:<token>@host/<repo>.git`.
-    /// The user comes from `HIVE_LABEL` (the agent's forge login),
-    /// falling back to `oauth2` which Forgejo also accepts as the
-    /// token-bearer username. Used by `clone` to clone/push.
+    /// The *credential-free* git URL for `repo` — no user/token in the
+    /// authority, so nothing durable lands in `.git/config` when this is
+    /// the URL `git clone` is given. Pairs with the `credential-helper`
+    /// verb, which `clone` configures as the repo's `credential.helper`
+    /// so git asks for (and gets) the token fresh from its file on every
+    /// fetch/push instead of it being embedded here. Replaces the old
+    /// `authed_git_url` (`http://<user>:<token>@host/<repo>.git`), which
+    /// left a durable token in every checkout's `.git/config` — a real
+    /// leak reported by atlas.
     #[must_use]
-    pub fn authed_git_url(&self, repo: &str) -> String {
-        let user = std::env::var("HIVE_LABEL").unwrap_or_else(|_| "oauth2".to_owned());
-        // Split scheme from authority so credentials land in the right spot.
-        let (scheme, host) = self
-            .base
-            .split_once("://")
-            .unwrap_or(("http", self.base.as_str()));
-        format!("{scheme}://{user}:{}@{host}/{repo}.git", self.token)
+    pub fn plain_git_url(&self, repo: &str) -> String {
+        format!("{}/{repo}.git", self.base)
+    }
+
+    /// The `-f/--forge` label this client resolved against (`None` for
+    /// the internal forge). See the `forge_label` field doc for why
+    /// `clone` needs this.
+    #[must_use]
+    pub fn forge_label(&self) -> Option<&str> {
+        self.forge_label.as_deref()
     }
 
     /// True when the operator passed the global `--json` flag.
@@ -331,7 +338,7 @@ pub fn index(n: u64) -> Result<i64> {
 /// `/` or `..`) is rejected up front with the same charset spelled out,
 /// rather than silently building a nonsense/traversing path and
 /// surfacing a confusing file error later.
-fn resolve_credentials(forge_label: Option<&str>) -> Result<(String, String)> {
+pub(crate) fn resolve_credentials(forge_label: Option<&str>) -> Result<(String, String)> {
     let Some(label) = forge_label else {
         let base = std::env::var("HIVE_FORGE_URL").unwrap_or_else(|_| DEFAULT_URL.to_owned());
         let token = read_token().context("read forge-token")?;

hive-forge/src/main.rs

@@ -176,6 +176,13 @@ enum Verb {
     /// Re-run CI without an empty commit. Pass one of `--pr <n>`,
     /// `--run <n>`, or `--branch <name>`; `--workflow` defaults to `ci.yml`.
     CiRerun(verbs::ci_rerun::Args),
+    /// Git credential-helper protocol (`get|store|erase`) — not a verb
+    /// you run by hand. `clone` configures each checkout's
+    /// `credential.helper` to invoke this, so git asks it for a token
+    /// fresh on every fetch/push instead of one being embedded in the
+    /// remote URL.
+    #[command(hide = true)]
+    CredentialHelper(verbs::credential_helper::Args),
 }
 
 /// Wrapper over [`run`] that owns how a failure reaches the operator.
@@ -197,6 +204,14 @@ fn main() -> ExitCode {
 
 fn run() -> Result<()> {
     let cli = Cli::parse();
+    let verb = cli.verb;
+    // `credential-helper` bypasses the normal client construction below:
+    // it needs no repo (unlike `Client::from_env`, which errors without
+    // one), and git may invoke it from a directory that isn't a resolved
+    // checkout yet (mid-`clone`, before the destination exists).
+    if let Verb::CredentialHelper(args) = verb {
+        return verbs::credential_helper::run(args, cli.forge.as_deref());
+    }
     let client = client::Client::from_env(cli.repo, cli.json, cli.forge)
         .context("initialize forge client")?;
     // Attach the resolved repo to every verb's error uniformly here,
@@ -211,7 +226,7 @@ fn run() -> Result<()> {
     // line 1 column 0" into "repo typo-org/repo: EOF while parsing a
     // value at line 1 column 0", which is diagnosable on sight.
     let repo = client.repo().to_owned();
-    dispatch(&client, cli.verb).with_context(|| format!("repo {repo}"))
+    dispatch(&client, verb).with_context(|| format!("repo {repo}"))
 }
 
 fn dispatch(client: &client::Client, verb: Verb) -> Result<()> {
@@ -253,5 +268,8 @@ fn dispatch(client: &client::Client, verb: Verb) -> Result<()> {
         Verb::ArtifactGet(a) => verbs::artifact_get::run(client, a),
         Verb::CiLog(a) => verbs::ci_log::run(client, a),
         Verb::CiRerun(a) => verbs::ci_rerun::run(client, a),
+        Verb::CredentialHelper(_) => {
+            unreachable!("handled in `run` before client construction")
+        }
     }
 }

hive-forge/src/verbs/clone.rs

@@ -4,6 +4,15 @@
 //! `client::Client::from_env` for the full resolution chain). Pairs
 //! with `pr-create --agit`: clone, edit + commit normally, then open a
 //! PR via the `AGit` ref.
+//!
+//! The clone URL itself carries no credentials, and the resulting
+//! checkout's `.git/config` never gets one either: `-c
+//! credential.helper=!hive-forge credential-helper` (baked into the
+//! `git clone` invocation, which persists into the new repo's config)
+//! makes git ask the `credential-helper` verb for a fresh token on every
+//! subsequent fetch/push instead. Previously the token itself rode in
+//! the clone URL and landed, durably, in every checkout's `.git/config` —
+//! a real credential leaked to every clone on disk, reported by atlas.
 
 use std::process::Command;
 
@@ -40,9 +49,17 @@ pub fn run(client: &Client, args: Args) -> Result<()> {
             .map(str::to_owned)
             .with_context(|| format!("clone: cannot derive a destination dir from repo {repo}"))?,
     };
-    let url = client.authed_git_url(repo);
+    let url = client.plain_git_url(repo);
+    let helper = match client.forge_label() {
+        Some(label) => format!("!hive-forge credential-helper -f {label}"),
+        None => "!hive-forge credential-helper".to_owned(),
+    };
 
-    let mut git_args = vec!["clone".to_owned()];
+    let mut git_args = vec![
+        "clone".to_owned(),
+        "-c".to_owned(),
+        format!("credential.helper={helper}"),
+    ];
     if let Some(depth) = args.depth {
         git_args.push(format!("--depth={depth}"));
     }

hive-forge/src/verbs/credential_helper.rs

@@ -0,0 +1,80 @@
+//! `credential-helper <get|store|erase>` — implements git's
+//! credential-helper protocol (`gitcredentials(7)`) so a cloned repo's
+//! `.git/config` only ever holds a *reference* to this command, never
+//! the forge token itself. `clone` configures the new repo's
+//! `credential.helper` to invoke this subcommand; git then calls it
+//! fresh on every fetch/push, reading the token from its usual
+//! on-disk location (the per-agent `forge-token` file, or the
+//! `--forge <label>` sidecar) at auth time rather than the token
+//! having been baked into the remote URL and left durably in
+//! `.git/config`. A real leak of that shape, found and reported by
+//! atlas, is what this verb exists to close.
+//!
+//! Deliberately bypasses the normal `Client::from_env` construction in
+//! `main.rs` (see the special-case there): that path requires resolving
+//! an active repo, which can fail depending on where git happens to run
+//! this helper from (e.g. mid-`clone`, before the destination checkout
+//! exists) — and a credential lookup has no need for a repo anyway.
+//!
+//! Only `get` does anything: reads the `key=value` lines git sends on
+//! stdin, and if a `host=` line is present, refuses to answer unless it
+//! matches the resolved forge's own host (defence in depth against this
+//! helper ever being invoked outside the specific-URL scope `clone`
+//! configures it under). `store`/`erase` drain stdin and no-op — there
+//! is nothing durable to store or erase, the token always comes fresh
+//! from its file.
+
+use std::io::Read;
+
+use anyhow::{Context, Result, bail};
+use clap::{Args as ClapArgs, ValueEnum};
+
+use crate::client::resolve_credentials;
+
+#[derive(ClapArgs)]
+pub struct Args {
+    /// The git credential-protocol operation git invokes this with.
+    op: Op,
+}
+
+#[derive(Clone, Copy, ValueEnum)]
+enum Op {
+    Get,
+    Store,
+    Erase,
+}
+
+/// # Errors
+///
+/// Returns an error if credential resolution fails (no token
+/// provisioned for the active forge) or the `get` request's stdin
+/// can't be read, or if a `host=` line in the request doesn't match
+/// the resolved forge.
+pub fn run(args: Args, forge_label: Option<&str>) -> Result<()> {
+    let mut input = String::new();
+    std::io::stdin()
+        .read_to_string(&mut input)
+        .context("read credential request from stdin")?;
+    let Op::Get = args.op else {
+        // `store`/`erase`: protocol says read the request, do nothing.
+        return Ok(());
+    };
+
+    let (base, token) = resolve_credentials(forge_label)?;
+    if let Some(requested) = input.lines().find_map(|l| l.strip_prefix("host=")) {
+        let expected = url::Url::parse(&base)
+            .ok()
+            .and_then(|u| u.host_str().map(str::to_owned));
+        if expected.is_some_and(|e| e != requested.trim()) {
+            bail!(
+                "hive-forge credential-helper: refusing to hand the forge token to \
+                 host {requested:?} (configured forge is {base:?})"
+            );
+        }
+    }
+
+    let user = std::env::var("HIVE_LABEL").unwrap_or_else(|_| "oauth2".to_owned());
+    println!("username={user}");
+    println!("password={token}");
+    Ok(())
+}

hive-forge/src/verbs/mod.rs

@@ -16,6 +16,7 @@ pub mod comment;
 pub mod comment_edit;
 pub mod comment_show;
 pub mod comments;
+pub mod credential_helper;
 pub mod dependency;
 pub mod diff;
 pub mod issue;