fabro/crates/arc-workflows/src/github_app.rs

use serde::Deserialize;

const GITHUB_API_BASE_URL: &str = "https://api.github.com";

/// Credentials for authenticating as a GitHub App.
#[derive(Clone, Debug)]
pub struct GitHubAppCredentials {
    pub app_id: String,
    pub private_key_pem: String,
}

/// Parse `owner` and `repo` from a GitHub HTTPS URL.
///
/// Accepts URLs like:
/// - `https://github.com/owner/repo.git`
/// - `https://github.com/owner/repo`
/// - `https://github.com/owner/repo/`
pub fn parse_github_owner_repo(url: &str) -> Result<(String, String), String> {
    let path = url
        .strip_prefix("https://github.com/")
        .ok_or_else(|| format!("Not a GitHub HTTPS URL: {url}"))?;

    let path = path.trim_end_matches('/');
    let path = path.strip_suffix(".git").unwrap_or(path);

    let mut parts = path.splitn(3, '/');
    let owner = parts
        .next()
        .filter(|s| !s.is_empty())
        .ok_or_else(|| format!("Missing owner in GitHub URL: {url}"))?;
    let repo = parts
        .next()
        .filter(|s| !s.is_empty())
        .ok_or_else(|| format!("Missing repo in GitHub URL: {url}"))?;

    Ok((owner.to_string(), repo.to_string()))
}

/// Create a signed JWT for GitHub App authentication (RS256).
///
/// The JWT is valid for 10 minutes with a 60-second clock skew allowance.
pub fn sign_app_jwt(app_id: &str, private_key_pem: &str) -> Result<String, String> {
    use jsonwebtoken::{encode, Algorithm, EncodingKey, Header};
    use serde::Serialize;

    #[derive(Serialize)]
    struct Claims {
        iss: String,
        iat: i64,
        exp: i64,
    }

    let now = chrono::Utc::now().timestamp();
    let claims = Claims {
        iss: app_id.to_string(),
        iat: now - 60,
        exp: now + 600,
    };

    let key = EncodingKey::from_rsa_pem(private_key_pem.as_bytes())
        .map_err(|e| format!("Invalid RSA private key: {e}"))?;

    encode(&Header::new(Algorithm::RS256), &claims, &key)
        .map_err(|e| format!("Failed to sign JWT: {e}"))
}

/// Check whether a GitHub repository is public using the App JWT.
pub async fn is_repo_public(
    jwt: &str,
    owner: &str,
    repo: &str,
    base_url: &str,
) -> Result<bool, String> {
    #[derive(Deserialize)]
    struct RepoResponse {
        private: bool,
    }

    let url = format!("{base_url}/repos/{owner}/{repo}");
    let client = reqwest::Client::new();
    let response = client
        .get(&url)
        .header("Authorization", format!("Bearer {jwt}"))
        .header("Accept", "application/vnd.github+json")
        .header("User-Agent", "arc")
        .send()
        .await
        .map_err(|e| format!("Failed to check repo visibility: {e}"))?;

    if response.status() == reqwest::StatusCode::NOT_FOUND {
        return Ok(false);
    }

    let body: RepoResponse = response
        .json()
        .await
        .map_err(|e| format!("Failed to parse repo response: {e}"))?;

    Ok(!body.private)
}

/// Request a scoped Installation Access Token for a specific repository.
///
/// Uses the App JWT to find the installation for `owner/repo`, then requests
/// a token scoped to `contents: read` on that single repository.
pub async fn create_installation_access_token(
    jwt: &str,
    owner: &str,
    repo: &str,
    base_url: &str,
) -> Result<String, String> {
    #[derive(Deserialize)]
    struct Installation {
        id: u64,
    }

    #[derive(Deserialize)]
    struct AccessToken {
        token: String,
    }

    let client = reqwest::Client::new();

    // Step 1: Find the installation for this repo
    let install_url = format!("{base_url}/repos/{owner}/{repo}/installation");
    let install_resp = client
        .get(&install_url)
        .header("Authorization", format!("Bearer {jwt}"))
        .header("Accept", "application/vnd.github+json")
        .header("User-Agent", "arc")
        .send()
        .await
        .map_err(|e| format!("Failed to look up GitHub App installation: {e}"))?;

    let status = install_resp.status();
    match status.as_u16() {
        200 => {}
        404 => {
            return Err(format!(
                "GitHub App is not installed for {owner}. \
                 Install it at https://github.com/organizations/{owner}/settings/installations"
            ));
        }
        403 => {
            return Err(
                "GitHub App installation is suspended. \
                 Re-enable it in your organization's GitHub App settings."
                    .to_string(),
            );
        }
        401 => {
            return Err(
                "GitHub App authentication failed. \
                 Check that app_id and GITHUB_APP_PRIVATE_KEY are correct."
                    .to_string(),
            );
        }
        _ => {
            return Err(format!(
                "Unexpected status {status} looking up GitHub App installation"
            ));
        }
    }

    let installation: Installation = install_resp
        .json()
        .await
        .map_err(|e| format!("Failed to parse installation response: {e}"))?;

    // Step 2: Create a scoped access token
    let token_url = format!(
        "{base_url}/app/installations/{}/access_tokens",
        installation.id
    );
    let body = serde_json::json!({
        "repositories": [repo],
        "permissions": { "contents": "read" }
    });

    let token_resp = client
        .post(&token_url)
        .header("Authorization", format!("Bearer {jwt}"))
        .header("Accept", "application/vnd.github+json")
        .header("User-Agent", "arc")
        .json(&body)
        .send()
        .await
        .map_err(|e| format!("Failed to create installation access token: {e}"))?;

    let token_status = token_resp.status();
    match token_status.as_u16() {
        201 => {}
        422 => {
            return Err(format!(
                "GitHub App does not have access to repository {repo}. \
                 Update the installation's repository permissions to include it."
            ));
        }
        401 => {
            return Err(
                "GitHub App authentication failed. \
                 Check that app_id and GITHUB_APP_PRIVATE_KEY are correct."
                    .to_string(),
            );
        }
        _ => {
            return Err(format!(
                "Unexpected status {token_status} creating installation access token"
            ));
        }
    }

    let access_token: AccessToken = token_resp
        .json()
        .await
        .map_err(|e| format!("Failed to parse access token response: {e}"))?;

    Ok(access_token.token)
}

/// Resolve git clone credentials for a GitHub repository.
///
/// Returns `(username, password)` for authenticated cloning, or `(None, None)`
/// for public repositories.
pub async fn resolve_clone_credentials(
    creds: &GitHubAppCredentials,
    owner: &str,
    repo: &str,
) -> Result<(Option<String>, Option<String>), String> {
    let jwt = sign_app_jwt(&creds.app_id, &creds.private_key_pem)?;

    if is_repo_public(&jwt, owner, repo, GITHUB_API_BASE_URL).await? {
        return Ok((None, None));
    }

    let token =
        create_installation_access_token(&jwt, owner, repo, GITHUB_API_BASE_URL).await?;
    Ok((
        Some("x-access-token".to_string()),
        Some(token),
    ))
}

#[cfg(test)]
mod tests {
    use super::*;

    // -----------------------------------------------------------------------
    // parse_github_owner_repo
    // -----------------------------------------------------------------------

    #[test]
    fn parse_https_with_git_suffix() {
        let (owner, repo) = parse_github_owner_repo("https://github.com/owner/repo.git").unwrap();
        assert_eq!(owner, "owner");
        assert_eq!(repo, "repo");
    }

    #[test]
    fn parse_https_without_git_suffix() {
        let (owner, repo) = parse_github_owner_repo("https://github.com/owner/repo").unwrap();
        assert_eq!(owner, "owner");
        assert_eq!(repo, "repo");
    }

    #[test]
    fn parse_https_with_trailing_slash() {
        let (owner, repo) = parse_github_owner_repo("https://github.com/owner/repo/").unwrap();
        assert_eq!(owner, "owner");
        assert_eq!(repo, "repo");
    }

    #[test]
    fn parse_non_github_url_errors() {
        let result = parse_github_owner_repo("https://gitlab.com/owner/repo");
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("Not a GitHub HTTPS URL"));
    }

    #[test]
    fn parse_missing_repo_errors() {
        let result = parse_github_owner_repo("https://github.com/owner");
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("Missing repo"));
    }

    #[test]
    fn parse_empty_string_errors() {
        let result = parse_github_owner_repo("");
        assert!(result.is_err());
    }

    // -----------------------------------------------------------------------
    // sign_app_jwt
    // -----------------------------------------------------------------------

    fn test_rsa_key() -> String {
        use std::process::Command;
        let output = Command::new("openssl")
            .args(["genpkey", "-algorithm", "RSA", "-pkeyopt", "rsa_keygen_bits:2048"])
            .output()
            .expect("openssl should be available");
        assert!(output.status.success(), "openssl keygen failed");
        String::from_utf8(output.stdout).unwrap()
    }

    #[test]
    fn jwt_is_three_part_string() {
        let pem = test_rsa_key();
        let jwt = sign_app_jwt("12345", &pem).unwrap();
        assert_eq!(jwt.split('.').count(), 3);
    }

    #[test]
    fn jwt_has_rs256_header() {
        let pem = test_rsa_key();
        let jwt = sign_app_jwt("12345", &pem).unwrap();
        let header_b64 = jwt.split('.').next().unwrap();
        let header_json =
            base64::Engine::decode(&base64::engine::general_purpose::URL_SAFE_NO_PAD, header_b64)
                .unwrap();
        let header: serde_json::Value = serde_json::from_slice(&header_json).unwrap();
        assert_eq!(header["alg"], "RS256");
    }

    #[test]
    fn jwt_has_correct_claims() {
        let pem = test_rsa_key();
        let jwt = sign_app_jwt("99999", &pem).unwrap();
        let payload_b64 = jwt.split('.').nth(1).unwrap();
        let payload_json =
            base64::Engine::decode(&base64::engine::general_purpose::URL_SAFE_NO_PAD, payload_b64)
                .unwrap();
        let claims: serde_json::Value = serde_json::from_slice(&payload_json).unwrap();
        assert_eq!(claims["iss"], "99999");

        let now = chrono::Utc::now().timestamp();
        let iat = claims["iat"].as_i64().unwrap();
        let exp = claims["exp"].as_i64().unwrap();
        // iat should be ~60s before now
        assert!((now - 60 - iat).abs() < 5);
        // exp should be ~10min after now
        assert!((now + 600 - exp).abs() < 5);
    }

    #[test]
    fn jwt_invalid_pem_errors() {
        let result = sign_app_jwt("12345", "not-a-pem");
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("Invalid RSA private key"));
    }

    // -----------------------------------------------------------------------
    // is_repo_public (mockito)
    // -----------------------------------------------------------------------

    #[tokio::test]
    async fn is_repo_public_returns_true_for_public() {
        let mut server = mockito::Server::new_async().await;
        let mock = server
            .mock("GET", "/repos/owner/repo")
            .match_header("Authorization", "Bearer test-jwt")
            .with_status(200)
            .with_body(r#"{"private": false}"#)
            .create_async()
            .await;

        let result = is_repo_public("test-jwt", "owner", "repo", &server.url()).await;
        assert_eq!(result.unwrap(), true);
        mock.assert_async().await;
    }

    #[tokio::test]
    async fn is_repo_public_returns_false_for_private() {
        let mut server = mockito::Server::new_async().await;
        let mock = server
            .mock("GET", "/repos/owner/repo")
            .with_status(200)
            .with_body(r#"{"private": true}"#)
            .create_async()
            .await;

        let result = is_repo_public("test-jwt", "owner", "repo", &server.url()).await;
        assert_eq!(result.unwrap(), false);
        mock.assert_async().await;
    }

    #[tokio::test]
    async fn is_repo_public_returns_false_for_404() {
        let mut server = mockito::Server::new_async().await;
        let mock = server
            .mock("GET", "/repos/owner/repo")
            .with_status(404)
            .create_async()
            .await;

        let result = is_repo_public("test-jwt", "owner", "repo", &server.url()).await;
        assert_eq!(result.unwrap(), false);
        mock.assert_async().await;
    }

    // -----------------------------------------------------------------------
    // create_installation_access_token — success
    // -----------------------------------------------------------------------

    #[tokio::test]
    async fn create_iat_success() {
        let mut server = mockito::Server::new_async().await;

        let install_mock = server
            .mock("GET", "/repos/owner/repo/installation")
            .match_header("Authorization", "Bearer test-jwt")
            .with_status(200)
            .with_body(r#"{"id": 123}"#)
            .create_async()
            .await;

        let token_mock = server
            .mock("POST", "/app/installations/123/access_tokens")
            .match_header("Authorization", "Bearer test-jwt")
            .match_body(mockito::Matcher::JsonString(
                r#"{"repositories":["repo"],"permissions":{"contents":"read"}}"#.to_string(),
            ))
            .with_status(201)
            .with_body(r#"{"token": "ghs_xxx"}"#)
            .create_async()
            .await;

        let token =
            create_installation_access_token("test-jwt", "owner", "repo", &server.url())
                .await
                .unwrap();
        assert_eq!(token, "ghs_xxx");

        install_mock.assert_async().await;
        token_mock.assert_async().await;
    }

    // -----------------------------------------------------------------------
    // create_installation_access_token — failure modes
    // -----------------------------------------------------------------------

    #[tokio::test]
    async fn create_iat_not_installed() {
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/repos/owner/repo/installation")
            .with_status(404)
            .create_async()
            .await;

        let err = create_installation_access_token("jwt", "owner", "repo", &server.url())
            .await
            .unwrap_err();
        assert!(err.contains("not installed"), "got: {err}");
        assert!(err.contains("owner"), "got: {err}");
    }

    #[tokio::test]
    async fn create_iat_suspended() {
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/repos/owner/repo/installation")
            .with_status(403)
            .create_async()
            .await;

        let err = create_installation_access_token("jwt", "owner", "repo", &server.url())
            .await
            .unwrap_err();
        assert!(err.contains("suspended"), "got: {err}");
    }

    #[tokio::test]
    async fn create_iat_no_repo_access() {
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/repos/owner/repo/installation")
            .with_status(200)
            .with_body(r#"{"id": 123}"#)
            .create_async()
            .await;
        server
            .mock("POST", "/app/installations/123/access_tokens")
            .with_status(422)
            .create_async()
            .await;

        let err = create_installation_access_token("jwt", "owner", "repo", &server.url())
            .await
            .unwrap_err();
        assert!(err.contains("does not have access"), "got: {err}");
        assert!(err.contains("repo"), "got: {err}");
    }

    #[tokio::test]
    async fn create_iat_auth_failed() {
        let mut server = mockito::Server::new_async().await;
        server
            .mock("GET", "/repos/owner/repo/installation")
            .with_status(401)
            .create_async()
            .await;

        let err = create_installation_access_token("jwt", "owner", "repo", &server.url())
            .await
            .unwrap_err();
        assert!(err.contains("authentication failed"), "got: {err}");
    }
}