add initial authentication types and filesystem stat trait method

gitbutler-git/src/backend/cli/executor.rs

@@ -127,6 +127,34 @@ pub unsafe trait GitExecutor {
     /// If for some reason these invariants are not possible to uphold,
     /// please open an issue on the repository to discuss this issue.
     async unsafe fn create_askpass_server<F>(&self) -> Result<Self::ServerHandle, Self::Error>;
+
+    /// Gets some basic information about a file on the filesystem.
+    ///
+    /// This is used to perform some basic security checks
+    /// during askpass authentication.
+    ///
+    /// **Do not follow symbolic links.**
+    async fn stat(&self, path: &str) -> Result<FileStat, Self::Error>;
+}
+
+/// Stats for a file on the filesystem.
+///
+/// This is returned by [`GitExecutor::stat`],
+/// and is just a small subset of the information
+/// typically returned by `stat(2)` and the like,
+/// as we only need a small subset of the information
+/// to perform some baseline security checks during
+/// the authentication process.
+#[derive(Debug, Clone)]
+pub struct FileStat {
+    /// The device number of the filesystem containing the file.
+    ///
+    /// On Windows, this is (probably) always 0.
+    pub dev: u64,
+    /// The inode number of the file.
+    pub ino: u64,
+    /// If the file is a regular file (not a symlink).
+    pub is_regular_file: bool,
 }
 
 /// A handle to a server created by [`GitExecutor::create_askpass_server`].

gitbutler-git/src/backend/cli/executor/tokio.rs

@@ -2,6 +2,8 @@
 
 use crate::prelude::*;
 use core::time::Duration;
+#[cfg(unix)]
+use std::os::unix::fs::MetadataExt;
 use std::{fs::Permissions, os::unix::fs::PermissionsExt};
 use tokio::process::Command;
 
@@ -48,6 +50,17 @@ unsafe impl super::GitExecutor for TokioExecutor {
             connection_string: connection_string.to_string_lossy().into(),
         })
     }
+
+    #[cfg(unix)]
+    async fn stat(&self, path: &str) -> Result<super::FileStat, Self::Error> {
+        let metadata = tokio::fs::symlink_metadata(path).await?;
+
+        Ok(super::FileStat {
+            dev: metadata.dev(),
+            ino: metadata.ino(),
+            is_regular_file: metadata.is_file(),
+        })
+    }
 }
 
 #[cfg(unix)]

gitbutler-git/src/lib.rs

@@ -52,5 +52,5 @@ pub use backend::git2;
 
 pub use self::{
     refspec::{Error as RefSpecError, RefSpec},
-    repository::{ConfigScope, Repository},
+    repository::{Authorization, ConfigScope, Repository},
 };

gitbutler-git/src/repository.rs

@@ -59,3 +59,37 @@ pub trait Repository {
         scope: ConfigScope,
     ) -> Result<(), Self::Error>;
 }
+
+/// Provides authentication credentials when performing
+/// an operation that interacts with a remote.
+#[derive(Default, Debug, Clone, PartialEq, Eq, Hash)]
+pub enum Authorization {
+    /// Performs no attempt to authorize; uses the system's
+    /// default authorization mechanism, if any.
+    #[default]
+    Auto,
+    /// Performs HTTP(S) Basic authentication with a username
+    /// and password.
+    ///
+    /// Note that certain remotes may use this mechanism
+    /// for passing tokens as well; consult the respective
+    /// remote's documentation for what information to supply.
+    Basic {
+        /// The username to use for authentication.
+        username: String,
+        /// The password to use for authentication.
+        password: String,
+    },
+    /// Specifies a set of credentials for logging in with SSH.
+    /// If
+    Ssh {
+        /// The path to the SSH private key to use for authentication.
+        /// If `None`, the default SSH key will be used (i.e. `-i` will not
+        /// be passed to `ssh`).
+        private_key: Option<String>,
+        /// The passphrase to use for the SSH private key.
+        /// If `None`, the key is assumed to be unencrypted.
+        /// A prompt for a passphrase will result in an error.
+        passphrase: Option<String>,
+    },
+}