api: add specific connection checking with job token

CHANGELOG.md

+# v0.1609.2 (unreleased)
+
+## Fixes
+
+  * Job token authentication is now compliant with its limited permissions.
+
 # v0.1609.1
 
 ## Fixes

src/auth.rs

@@ -7,8 +7,10 @@
 use http::{HeaderMap, HeaderValue};
 use log::error;
 use serde::Deserialize;
+use std::env;
 use thiserror::Error;
 
+use crate::api::projects::packages::Packages;
 use crate::api::users::CurrentUser;
 use crate::api::{self, AsyncQuery, Query};
 
@@ -20,6 +22,22 @@ pub enum AuthError {
         #[from]
         source: http::header::InvalidHeaderValue,
     },
+    /// The CI environment is misconfigured
+    #[error("CI environment is missing `CI_PROJECT_ID`")]
+    CiEnvironmentMissing,
+    /// The CI environment is misconfigured
+    #[error("CI environment has a non-integer `CI_PROJECT_ID`")]
+    CiEnvironmentInvalid,
+}
+
+impl AuthError {
+    fn ci_environment_missing() -> Self {
+        Self::CiEnvironmentMissing
+    }
+
+    fn ci_environment_invalid() -> Self {
+        Self::CiEnvironmentInvalid
+    }
 }
 
 #[derive(Deserialize, Debug)]
@@ -29,6 +47,13 @@ struct UserPublic {
     _username: String,
 }
 
+#[derive(Deserialize, Debug)]
+struct ProjectPackage {
+    /// The username.
+    #[serde(rename = "id")]
+    _id: u64,
+}
+
 type AuthResult<T> = Result<T, AuthError>;
 
 /// A Gitlab API token
@@ -85,11 +110,22 @@ impl Auth {
     where
         C: api::Client,
     {
-        if let Self::None = self {
-            // There does not seem to be an unparameterized endpoint that can be used to reliably
-            // detect whether the connection will work or not.
-        } else {
-            let _: UserPublic = CurrentUser::builder().build().unwrap().query(api)?;
+        match self {
+            Self::None => {
+                // There does not seem to be an unparameterized endpoint that can be used to reliably
+                // detect whether the connection will work or not.
+            },
+            Self::JobToken(_) => {
+                let project_id = Self::_ci_project_id()?;
+                let _: Vec<ProjectPackage> = Packages::builder()
+                    .project(project_id)
+                    .build()
+                    .unwrap()
+                    .query(api)?;
+            },
+            Self::Token(_) | Self::OAuth2(_) => {
+                let _: UserPublic = CurrentUser::builder().build().unwrap().query(api)?;
+            },
         }
 
         Ok(())
@@ -99,17 +135,36 @@ impl Auth {
     where
         C: api::AsyncClient + Sync,
     {
-        if let Self::None = self {
-            // There does not seem to be an unparameterized endpoint that can be used to reliably
-            // detect whether the connection will work or not.
-        } else {
-            let _: UserPublic = CurrentUser::builder()
-                .build()
-                .unwrap()
-                .query_async(api)
-                .await?;
+        match self {
+            Self::None => {
+                // There does not seem to be an unparameterized endpoint that can be used to reliably
+                // detect whether the connection will work or not.
+            },
+            Self::JobToken(_) => {
+                let project_id = Self::_ci_project_id()?;
+                let _: Vec<ProjectPackage> = Packages::builder()
+                    .project(project_id)
+                    .build()
+                    .unwrap()
+                    .query_async(api)
+                    .await?;
+            },
+            Self::Token(_) | Self::OAuth2(_) => {
+                let _: UserPublic = CurrentUser::builder()
+                    .build()
+                    .unwrap()
+                    .query_async(api)
+                    .await?;
+            },
         }
 
         Ok(())
     }
+
+    fn _ci_project_id() -> Result<u64, AuthError> {
+        env::var("CI_PROJECT_ID")
+            .map_err(|_| AuthError::ci_environment_missing())?
+            .parse::<u64>()
+            .map_err(|_| AuthError::ci_environment_invalid())
+    }
 }