test: configure git for local testing

There is a local credential helper and JWT creation utility: this envrc configures git to override the current configuration via environment variables. The local testing server is used instead.

.development/.envrc

@@ -1,13 +1,35 @@
-#!/bin/sh
+#!/bin/bash
+
+# This configuration allows for local testing of the bridge. It uses Git config
+# environment variables to override local configuration without making changes
+# to it. See https://git-scm.com/docs/git-config#ENVIRONMENT
+
+git_config_add() {
+    local key="$1"
+    local value="$2"
+
+    index=$(( "${GIT_CONFIG_COUNT:-0}" - 1 ))
+
+    # index is incremented each time a setting is added
+    index=$(( index + 1 ))
+    export GIT_CONFIG_COUNT=$(( index + 1 ))
+    export "GIT_CONFIG_KEY_${index}=${key}"
+    export "GIT_CONFIG_VALUE_${index}=${value}"
+}
 
-# default values
-export GIT_CONFIG_COUNT=2
-export GIT_CONFIG_KEY_0="credential.https://github.com.usehttppath"
-export GIT_CONFIG_VALUE_0="true"
 helper_path="$(expand_path ../helper)"
-export GIT_CONFIG_KEY_1="credential.https://github.com.helper"
-export GIT_CONFIG_VALUE_1="${helper_path}/buildkite-connector-credential-helper http://localhost:${SERVER_PORT:-8080}/credential-helper"
 
+# Use the empty string to override helpers from other configuration
+# See https://git-scm.com/docs/gitcredentials/2.29.0#Documentation/gitcredentials.txt-helper
+git_config_add "credential.helper" ""
+git_config_add "credential.https://github.com.helper" ""
+
+# Now configure the testing helper from the this repo. This uses the local JWT
+# keys to create an OIDC token that mimics Buildkite's, but doesn't require a
+# Buildkite agent. It only works if the server is run with the corresponding
+# test keys; see the root .envrc for that information.
+git_config_add "credential.https://github.com.helper" "${helper_path}/buildkite-connector-credential-helper http://localhost:${SERVER_PORT:-8080}/git-credentials"
+git_config_add "credential.https://github.com.usehttppath" "true"
 
 source_up
 
@@ -21,9 +43,15 @@ source_env_if_exists ".envrc.private"
 #
 # Git diagnostics
 #
+# Useful git variables for understanding if the credential helper is working.
+#
 
-# useful git variables for understanding if the credential helper is working
+# trace will show the credential commands that are executed
 # export GIT_TRACE=2
+
+# like curl -v, but for git
 # export GIT_CURL_VERBOSE=1
+
+# unsure about the value of this one
 # export GIT_TRACE_PACKET=1