n0-computer · Frando · Mar 25, 2025
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -19,8 +19,15 @@ hex = "0.4.3"
 postcard = { version = "1.1.1", features = ["use-std"] }
 rand = "0.8.5"
 serde = { version = "1.0.217", features = ["derive"] }
+ssh-encoding = { version = "0.2.0", features = ["pem", "std"], optional = true }
+tokio = { version = "1", optional = true, features = ["fs"] }
 
 [dev-dependencies]
 bitfields = "0.12.4"
 rand_chacha = "0.3.1"
 testresult = "0.4.1"
+
+[features]
+default = []
+fs = ["pem", "dep:tokio"]
+pem = ["dep:ssh-encoding"]
diff --git a/src/chain.rs b/src/chain.rs
@@ -0,0 +1,128 @@
+use std::time::Duration;
+
+use anyhow::{bail, ensure, Context, Result};
+use ed25519_dalek::{SigningKey, VerifyingKey};
+use serde::{de::DeserializeOwned, Deserialize, Serialize};
+
+use crate::{Authorizer, Capability, Expires, Rcan, VERSION};
+
+#[derive(Debug, Serialize, Deserialize, Eq, PartialEq, Clone)]
+pub struct RcanChain<C>(Vec<Rcan<C>>);
+
+impl<C> Default for RcanChain<C> {
+    fn default() -> Self {
+        Self(Vec::new())
+    }
+}
+
+impl<C: Capability> RcanChain<C> {
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn from_rcan(rcan: Rcan<C>) -> Self {
+        Self(vec![rcan])
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = &'_ Rcan<C>> + '_ {
+        self.into_iter()
+    }
+
+    pub fn first_issuer(&self) -> Result<&VerifyingKey> {
+        self.0
+            .first()
+            .map(|rcan| rcan.issuer())
+            .context("rcan chain is empty")
+    }
+
+    pub fn final_audience(&self) -> Result<&VerifyingKey> {
+        self.0
+            .last()
+            .map(|rcan| rcan.audience())
+            .context("rcan chain is empty")
+    }
+
+    pub fn final_capability(&self) -> Result<&C> {
+        self.0
+            .last()
+            .map(|rcan| rcan.capability())
+            .context("rcan chain is empty")
+    }
+
+    pub fn verify_chain(&self) -> Result<()> {
+        self.check_invocation_from(
+            *self.first_issuer()?,
+            *self.final_audience()?,
+            self.final_capability()?,
+        )
+    }
+
+    pub fn check_invocation_from(
+        &self,
+        root_issuer: VerifyingKey,
+        invoker: VerifyingKey,
+        capability: &C,
+    ) -> Result<()> {
+        if self.first_issuer()? != &root_issuer {
+            bail!("invocation failed: root issuer does not match");
+        }
+        Authorizer::new(root_issuer)
+            .check_invocation_from(invoker, capability, self)
+            .context("not authorized")?;
+        Ok(())
+    }
+
+    pub fn with_delegation(
+        &self,
+        issuer: &SigningKey,
+        audience: VerifyingKey,
+        capability: C,
+        max_age: Duration,
+    ) -> Result<Self>
+    where
+        C: Clone,
+    {
+        let root_issuer = self.first_issuer()?;
+        self.check_invocation_from(*root_issuer, issuer.verifying_key(), &capability)?;
+
+        let can = Rcan::delegating_builder(&issuer, audience, *root_issuer, capability)
+            .sign(Expires::valid_for(max_age));
+        let mut next_chain = self.0.clone();
+        next_chain.push(can);
+        Ok(Self(next_chain))
+    }
+
+    pub fn encode(&self) -> Vec<u8> {
+        postcard::to_extend(self, vec![VERSION]).expect("vec")
+    }
+
+    pub fn encoded_len(&self) -> usize {
+        postcard::experimental::serialized_size(self).unwrap() + 1
+    }
+
+    pub fn decode(bytes: &[u8]) -> Result<Self>
+    where
+        C: DeserializeOwned,
+    {
+        let Some(version) = bytes.first() else {
+            bail!("cannot decode, token is empty");
+        };
+        ensure!(*version == VERSION, "invalid version: {}", version);
+        let out: Self = postcard::from_bytes(&bytes[1..]).context("decoding")?;
+        Ok(out)
+    }
+}
+
+impl<'a, C> IntoIterator for &'a RcanChain<C> {
+    type Item = &'a Rcan<C>;
+
+    type IntoIter = std::slice::Iter<'a, Rcan<C>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0[..].into_iter()
+    }
+}