//! Certificates for short-lived keys (oxygenhub#241, docs/keyless.md,

//! Oxygen spec §14.7): the hub vouches, for ten minutes, for a fresh key

//! whose holder proves who it is with a credential the hub issued. A Flow

//! job asks with its job token; anything else with one of the hub's OIDC

//! tokens for the keyless audience. The key signs, then is thrown away:

//! nothing long-lived sits on a runner.

//!

//! An agent asks with a grant token instead (step 5): its owner signed an

//! Oxygen grant letting `agent:NAME@ACCOUNT` act for them (spec §14.7),

//! and every certificate issued under it carries that grant, so the

//! agent's fresh keys sign in the owner's name with nothing kept on disk

//! but the token. Revoking the grant stops the certificates.

use crate::api::ApiError;

use crate::{db, Shared};

use axum::extract::Path;

use axum::extract::State;

use axum::http::{HeaderMap, StatusCode};

use axum::Json;

use oxy_core::cert::{certify_challenge, Certificate, SignedCertificate, SignedGrant};

use oxy_core::identity::{verify_challenge, Identity, Scope, Signature};

use serde::{Deserialize, Serialize};

/// How long a certificate lasts.

pub const LIFETIME_MS: i64 = 10 * 60 * 1000;

/// How far back a certificate starts, for clocks a little behind.

const SKEW_MS: i64 = 30 * 1000;

/// What an agent holds in place of a key: `oxyagent_` and 32 random bytes.

pub const GRANT_TOKEN_PREFIX: &str = "oxyagent_";

/// The OIDC audience a token must have to be exchanged here.

pub fn audience(base_url: &str) -> String {

    format!("{}/keyless", base_url.trim_end_matches('/'))

}

#[derive(Deserialize)]

pub struct CertifyRequest {

    /// The fresh key's identity object, base64.

    pub identity: String,

    /// The key's signature over `certify_challenge(credential)`, base64 CBOR.

    pub proof: String,

    /// `changes,refs` and so on.

    pub scope: String,

}

#[derive(Serialize)]

pub struct CertifyResponse {

    /// The signed certificate, base64 (`[certificate, signature]`).

    pub certificate: String,

    pub subject: String,

    pub expires_ms: i64,

    /// For an agent's certificate, the identity that signed its grant

    /// (base64), so a repository that never saw the owner's current key can

    /// check the grant, and pass it on with its push (oxygen#134).

    #[serde(skip_serializing_if = "Option::is_none")]

    pub grantor_identity: Option<String>,

}

/// Who a credential says its holder is.

struct Proven {

    subject: String,

    claims: Vec<(String, String)>,

    /// The credential's own end, which a certificate never outlives.

    until_ms: i64,

    target: String,

    /// The most the certificate may give.

    allowed: Scope,

    /// The owner's grant the certificate carries, for an agent.

    grant: Option<SignedGrant>,

}

fn bad(status: StatusCode, why: impl Into<String>) -> ApiError {

    ApiError(status, why.into())

}

/// A running job's token: its repository, bookmark, run and job.

async fn job_proof(app: &Shared, token: &str) -> Result<Proven, ApiError> {

    let invalid = || bad(StatusCode::UNAUTHORIZED, "this job token is not valid (the job must be running)");

    let hash = crate::auth::token_hash(token);

    let job = db::flow::job_by_token(&app.db, &hash, crate::flow::JOB_TOKEN_MAX_AGE_MS)

        .await

        .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?

        .ok_or_else(invalid)?;

    let run = db::flow::run_by_id(&app.db, job.run_id)

        .await

        .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?

        .ok_or_else(invalid)?;

    let repo = db::repos::get_by_id(&app.db, run.repo_id)

        .await

        .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?

        .ok_or_else(invalid)?;

    let mut claims = vec![

        ("repository".to_string(), format!("{}/{}", repo.owner, repo.name)),

        ("bookmark".to_string(), run.bookmark.clone()),

        ("run".to_string(), run.number.to_string()),

        ("job".to_string(), job.name.clone()),

        ("runner".to_string(), job.runner.clone()),

    ];

    if !job.environment.is_empty() && !job.approved_by.is_empty() {

        claims.push(("environment".to_string(), job.environment.clone()));

        claims.push(("approved_by".to_string(), job.approved_by.clone()));

    }

    Ok(Proven {

        subject: format!("repo:{}/{}:bookmark:{}", repo.owner, repo.name, run.bookmark),

        claims,

        until_ms: job.started_ms.unwrap_or(0) + crate::flow::JOB_TOKEN_MAX_AGE_MS,

        target: format!("{}/{}", repo.owner, repo.name),

        allowed: Scope::CHANGES | Scope::REFS | Scope::SEAL,

        grant: None,

    })

}

/// One of this hub's OIDC tokens for the keyless audience.

async fn oidc_proof(app: &Shared, token: &str, now: i64) -> Result<Proven, ApiError> {

    let issuer = app.oidc().await.map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    let aud = audience(app.config.base_url());

    let claims = issuer

        .verify(token, &aud, now)

        .ok_or_else(|| bad(StatusCode::UNAUTHORIZED, format!("the token is not one of this hub's, for audience {aud}, still valid")))?;

    let subject = claims["sub"].as_str().unwrap_or("").to_string();

    if subject.is_empty() {

        return Err(bad(StatusCode::UNAUTHORIZED, "the token names no subject"));

    }

    let keep = ["repository", "bookmark", "run_number", "job", "runner", "environment", "approved_by"];

    let mut out = Vec::new();

    for k in keep {

        match &claims[k] {

            serde_json::Value::String(s) => out.push((k.to_string(), s.clone())),

            serde_json::Value::Number(n) => out.push((k.to_string(), n.to_string())),

            _ => {}

        }

    }

    Ok(Proven {

        target: claims["repository"].as_str().unwrap_or(&subject).to_string(),

        subject,

        claims: out,

        until_ms: claims["exp"].as_i64().unwrap_or(0) * 1000,

        allowed: Scope::CHANGES | Scope::REFS | Scope::SEAL,

        grant: None,

    })

}

/// An agent's grant token: the owner's live grant.

async fn grant_proof(app: &Shared, token: &str, now: i64) -> Result<Proven, ApiError> {

    let invalid = || bad(StatusCode::UNAUTHORIZED, "this agent grant is not valid (revoked, ended or unknown)");

    let g = db::accounts::agent_grant_by_token(&app.db, &crate::auth::token_hash(token))

        .await

        .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?

        .filter(|g| g.live(now))

        .ok_or_else(invalid)?;

    let signed = SignedGrant::decode(&g.signed).map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    db::accounts::touch_agent_grant(&app.db, g.id).await.ok();

    Ok(Proven {

        subject: g.subject.clone(),

        claims: vec![("agent".to_string(), g.agent.clone()), ("grant".to_string(), g.id.to_string())],

        until_ms: g.expires_ms,

        target: g.subject,

        allowed: signed.grant.scope,

        grant: Some(signed),

    })

}

/// `POST /api/v1/keyless/certify`: a ten-minute certificate for a fresh

/// key, for whoever the bearer credential proves.

pub async fn certify(

    State(app): State<Shared>,

    headers: HeaderMap,

    Json(req): Json<CertifyRequest>,

) -> Result<Json<CertifyResponse>, ApiError> {

    let token = oxy_server::bearer_token(&headers)

        .ok_or_else(|| bad(StatusCode::UNAUTHORIZED, "ask with a job token or one of this hub's OIDC tokens as the bearer"))?

        .to_string();

    let now = db::now_ms();

    let proven = if token.starts_with(crate::flow::JOB_TOKEN_PREFIX) {

        job_proof(&app, &token).await?

    } else if token.starts_with(GRANT_TOKEN_PREFIX) {

        grant_proof(&app, &token, now).await?

    } else {

        oidc_proof(&app, &token, now).await?

    };

    let decode = |what: &str, b64: &str| {

        oxy_core::dsse::base64_decode(b64.trim()).ok_or_else(|| bad(StatusCode::BAD_REQUEST, format!("{what} is not base64")))

    };

    let identity =

        Identity::decode(&decode("identity", &req.identity)?).map_err(|e| bad(StatusCode::BAD_REQUEST, format!("identity: {e}")))?;

    let proof = oxy_core::cbor::decode(&decode("proof", &req.proof)?)

        .map_err(|e| e.to_string())

        .and_then(|v| Signature::from_value(&v).map_err(|e| e.to_string()))

        .map_err(|e| bad(StatusCode::BAD_REQUEST, format!("proof: {e}")))?;

    verify_challenge(&identity, &proof, &certify_challenge(&token))

        .map_err(|e| bad(StatusCode::UNAUTHORIZED, format!("the proof does not show this key's holder asked: {e}")))?;

    // What was asked, within what the credential allows (an agent's grant

    // may leave out `refs`, say): a key asks for all it might sign.

    let asked = Scope::parse(&req.scope).map_err(|e| bad(StatusCode::BAD_REQUEST, e))?;

    let scope =

        asked.names().into_iter().filter_map(|n| Scope::parse(n).ok()).filter(|s| proven.allowed.has(*s)).fold(Scope::NONE, |a, s| a | s);

    if scope.is_empty() {

        return Err(bad(StatusCode::FORBIDDEN, format!("{} may be certified for {} only", proven.subject, proven.allowed)));

    }

    let expires = (now + LIFETIME_MS).min(proven.until_ms);

    if expires <= now {

        return Err(bad(StatusCode::UNAUTHORIZED, "the credential is about to expire: ask with a fresh one"));

    }

    let (key, secret) =

        crate::keys::load_secret(&app.config.keys_dir()).map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    let cert = Certificate {

        key: identity,

        issuer: key,

        subject: proven.subject.clone(),

        claims: proven.claims,

        scope,

        not_before: (now - SKEW_MS) as u64,

        expires: expires as u64,

        grant: proven.grant,

    };

    // The grant's signer, as linked to its account (the grant was checked

    // against it when it was made).

    let grantor_identity = match &cert.grant {

        Some(g) => db::accounts::identity_by_key(&app.db, &g.grant.grantor.to_hex())

            .await

            .ok()

            .flatten()

            .map(|l| oxy_core::dsse::base64(&l.object)),

        None => None,

    };

    let signed = SignedCertificate::sign(cert, &app.hub_key.identity, &secret);

    let detail = format!("{} for {} until {}", signed.cert.key_id().short(12), proven.subject, expires);

    db::accounts::audit(&app.db, None, "keyless.certified", &proven.target, &detail).await.ok();

    // Every certificate is logged (#238), as Fulcio's are in Rekor.

    crate::tlog::log(

        &app,

        vec![crate::tlog::Pending {

            kind: "certificate",

            repo: [0; 16],

            repo_row: None,

            object: signed.cert.hash(),

            signers: vec![app.hub_key.key],

        }],

    )

    .await;

    Ok(Json(CertifyResponse {

        certificate: oxy_core::dsse::base64(&signed.encode()),

        subject: proven.subject,

        expires_ms: expires,

        grantor_identity,

    }))

}

#[derive(Deserialize)]

pub struct GrantRequest {

    /// The signed Oxygen grant (`[grant, signature]`), base64.

    pub grant: String,

}

#[derive(Serialize)]

pub struct GrantView {

    pub id: i64,

    pub agent: String,

    pub subject: String,

    pub grantor: String,

    pub scope: String,

    pub created_ms: i64,

    pub expires_ms: i64,

    pub revoked_ms: Option<i64>,

    pub last_used_ms: Option<i64>,

    /// Shown once, when the grant is made.

    #[serde(skip_serializing_if = "Option::is_none")]

    pub token: Option<String>,

}

impl From<db::accounts::AgentGrant> for GrantView {

    fn from(g: db::accounts::AgentGrant) -> Self {

        GrantView {

            id: g.id,

            agent: g.agent,

            subject: g.subject,

            grantor: g.grantor,

            scope: g.scope,

            created_ms: g.created_ms,

            expires_ms: g.expires_ms,

            revoked_ms: g.revoked_ms,

            last_used_ms: g.last_used_ms,

            token: None,

        }

    }

}

/// The account behind a personal token. A grant needs no token scope:

/// what makes it is the owner's signature, by a key linked to the account.

async fn owner(app: &Shared, headers: &HeaderMap) -> Result<db::accounts::Account, ApiError> {

    let c = crate::api::caller(app, headers).await?;

    c.account.ok_or_else(|| bad(StatusCode::UNAUTHORIZED, "a personal access token is required"))

}

/// An agent's name: what follows `agent:` and precedes `@`.

fn agent_name_ok(name: &str) -> bool {

    !name.is_empty() && name.len() <= 64 && name.chars().all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_' || c == '.')

}

/// `POST /api/v1/agents/grants`: keep an owner's signed grant to one of

/// their agents and give the agent its token.

pub async fn grants_create(

    State(app): State<Shared>,

    headers: HeaderMap,

    Json(req): Json<GrantRequest>,

) -> Result<(StatusCode, Json<GrantView>), ApiError> {

    let account = owner(&app, &headers).await?;

    let bytes = oxy_core::dsse::base64_decode(req.grant.trim()).ok_or_else(|| bad(StatusCode::BAD_REQUEST, "the grant is not base64"))?;

    let signed = SignedGrant::decode(&bytes).map_err(|e| bad(StatusCode::BAD_REQUEST, format!("grant: {e}")))?;

    let g = &signed.grant;

    let suffix = format!("@{}", account.username);

    let agent = g

        .subject

        .strip_prefix("agent:")

        .and_then(|r| r.strip_suffix(&suffix))

        .filter(|n| agent_name_ok(n))

        .ok_or_else(|| bad(StatusCode::BAD_REQUEST, format!("a grant here is for agent:NAME{suffix}, not {}", g.subject)))?

        .to_string();

    if g.issuer != app.hub_key.key {

        return Err(bad(StatusCode::BAD_REQUEST, "the grant names another issuer than this hub's key (/.well-known/oxyhub-key)"));

    }

    let grantor = g.grantor.to_hex();

    let linked = db::accounts::identity_by_key(&app.db, &grantor)

        .await

        .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?

        .filter(|i| i.account_id == account.id)

        .ok_or_else(|| bad(StatusCode::FORBIDDEN, format!("key {} is not linked to your account: link it first", g.grantor.short(12))))?;

    let identity = Identity::decode(&linked.object).map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    signed.verify(&identity).map_err(|e| bad(StatusCode::BAD_REQUEST, format!("the grant does not verify: {e}")))?;

    let now = db::now_ms();

    if (g.expires as i64) <= now {

        return Err(bad(StatusCode::BAD_REQUEST, "the grant has already ended"));

    }

    let token = format!("{GRANT_TOKEN_PREFIX}{}", crate::auth::random_hex(32));

    let hash = crate::auth::token_hash(&token);

    let scope = g.scope.to_string();

    let id = db::accounts::create_agent_grant(

        &app.db,

        db::accounts::NewAgentGrant {

            account_id: account.id,

            agent: &agent,

            subject: &g.subject,

            grantor: &grantor,

            scope: &scope,

            signed: &bytes,

            token_hash: &hash,

            expires_ms: g.expires as i64,

        },

    )

    .await

    .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    db::accounts::audit(&app.db, Some(&account), "agent.granted", &g.subject, &format!("grant {id}, {scope}, until {}", g.expires))

        .await

        .ok();

    Ok((

        StatusCode::CREATED,

        Json(GrantView {

            id,

            agent,

            subject: g.subject.clone(),

            grantor,

            scope,

            created_ms: now,

            expires_ms: g.expires as i64,

            revoked_ms: None,

            last_used_ms: None,

            token: Some(token),

        }),

    ))

}

/// `GET /api/v1/agents/grants`: the caller's grants, without tokens.

pub async fn grants_list(State(app): State<Shared>, headers: HeaderMap) -> Result<Json<Vec<GrantView>>, ApiError> {

    let account = owner(&app, &headers).await?;

    let grants =

        db::accounts::agent_grants_of(&app.db, account.id).await.map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    Ok(Json(grants.into_iter().map(GrantView::from).collect()))

}

/// `DELETE /api/v1/agents/grants/{id}`: stop certifying under a grant.

pub async fn grants_revoke(State(app): State<Shared>, headers: HeaderMap, Path(id): Path<i64>) -> Result<StatusCode, ApiError> {

    let account = owner(&app, &headers).await?;

    let done = db::accounts::revoke_agent_grant(&app.db, account.id, id)

        .await

        .map_err(|e| bad(StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;

    if !done {

        return Err(bad(StatusCode::NOT_FOUND, "no such live grant of yours"));

    }

    db::accounts::audit(&app.db, Some(&account), "agent.revoked", &format!("grant {id}"), "").await.ok();

    Ok(StatusCode::NO_CONTENT)

}