fix: update expires_in for cached metadata-retrieved tokens (#464)

googleauth.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |gem|
   gem.required_ruby_version = ">= 2.7"
 
   gem.add_dependency "faraday", ">= 1.0", "< 3.a"
-  gem.add_dependency "google-cloud-env", "~> 2.0", ">= 2.0.1"
+  gem.add_dependency "google-cloud-env", "~> 2.1"
   gem.add_dependency "jwt", ">= 1.4", "< 3.0"
   gem.add_dependency "multi_json", "~> 1.11"
   gem.add_dependency "os", ">= 0.9", "< 2.0"

lib/googleauth/compute_engine.rb

@@ -95,7 +95,7 @@ def fetch_access_token _options = {}
           resp = Google::Cloud.env.lookup_metadata_response "instance", entry, query: query
           case resp.status
           when 200
-            build_token_hash resp.body, resp.headers["content-type"]
+            build_token_hash resp.body, resp.headers["content-type"], resp.retrieval_monotonic_time
           when 403, 500
             msg = "Unexpected error code #{resp.status} #{UNEXPECTED_ERROR_SUFFIX}"
             raise Signet::UnexpectedStatusError, msg
@@ -112,7 +112,7 @@ def fetch_access_token _options = {}
 
       private
 
-      def build_token_hash body, content_type
+      def build_token_hash body, content_type, retrieval_time
         hash =
           if ["text/html", "application/text"].include? content_type
             { token_type.to_s => body }
@@ -122,6 +122,15 @@ def build_token_hash body, content_type
         universe_domain = Google::Cloud.env.lookup_metadata "universe", "universe_domain"
         universe_domain = "googleapis.com" if !universe_domain || universe_domain.empty?
         hash["universe_domain"] = universe_domain.strip
+        # The response might have been cached, which means expires_in might be
+        # stale. Update it based on the time since the data was retrieved.
+        # We also ensure expires_in is conservative; subtracting at least 1
+        # second to offset any skew from metadata server latency.
+        if hash["expires_in"].is_a? Numeric
+          offset = 1 + (Process.clock_gettime(Process::CLOCK_MONOTONIC) - retrieval_time).round
+          hash["expires_in"] -= offset if offset.positive?
+          hash["expires_in"] = 0 if hash["expires_in"].negative?
+        end
         hash
       end
     end

spec/googleauth/compute_engine_spec.rb

@@ -77,6 +77,15 @@ def make_auth_stubs opts
       @client.fetch_access_token!
       expect(@client.universe_domain).to eq("googleapis.com")
     end
+
+    it "returns a consistent expiry using cached data" do
+      make_auth_stubs access_token: "1/abcde"
+      @client.fetch_access_token!
+      expiry = @client.expires_at
+      sleep 1
+      @client.fetch_access_token!
+      expect(@client.expires_at.to_f).to be_within(0.1).of(expiry.to_f)
+    end
   end
 
   context "custom universe" do

spec/googleauth/external_account_spec.rb

@@ -20,7 +20,7 @@
 
 describe Google::Auth::ExternalAccount::Credentials do
 
-  describe "universe_domain checks", :focus do
+  describe "universe_domain checks" do
     before :example do
       @tempfile = Tempfile.new("aws")
     end