configs: Improve security of in-repo configuration.

CHANGELOG.md

@@ -66,6 +66,11 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
   tags. These keywords may be useful in non-colocated Git repositories where
   local and exported `@git` tags can point to different revisions.
 
+* Per-repo configurations are now signed, preventing you from using
+  configurations created by another user. This means you must now use
+  `jj config edit` to edit in-repo configs instead of manually specifying the
+  path.
+
 ### Fixed bugs
 
 * `jj metaedit --author-timestamp` twice with the same value no longer

Cargo.toml

@@ -45,6 +45,7 @@ crossterm = { version = "0.28", default-features = false, features = ["windows"]
 datatest-stable = "0.3.3"
 digest = "0.10.7"
 dunce = "1.0.5"
+ed25519-dalek = { version = "3.0.0-pre.1", features = ["alloc", "pkcs8", "rand_core"] }
 erased-serde = "0.4.8"
 etcetera = "0.10.0"
 either = "1.15.0"
@@ -72,6 +73,7 @@ num_cpus = "1.17.0"
 once_cell = "1.21.3"
 pest = "2.8.3"
 pest_derive = "2.8.3"
+pkcs8 = { version = "0.11.0-rc.7", features = ["std"] }
 pollster = "0.4.0"
 pretty_assertions = "1.4.1"
 proc-macro2 = "1.0.96"

cli/Cargo.toml

@@ -82,6 +82,7 @@ once_cell = { workspace = true }
 pest = { workspace = true }
 pest_derive = { workspace = true }
 pollster = { workspace = true }
+prost = { workspace = true }
 rayon = { workspace = true }
 regex = { workspace = true }
 rpassword = { workspace = true }