Add config module

The config module supports adding configuration to the exporter via a config file. This supports adding authentication details in a config file so that /probe requests can specify authentication for endpoints

Signed-off-by: Joe Adams <github@joeadams.io>

config/config_test.go

@@ -0,0 +1,58 @@
+// Copyright 2022 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	"testing"
+)
+
+func TestLoadConfig(t *testing.T) {
+	ch := &ConfigHandler{
+		Config: &Config{},
+	}
+
+	err := ch.ReloadConfig("testdata/config-good.yaml", nil)
+	if err != nil {
+		t.Errorf("Error loading config: %s", err)
+	}
+}
+
+func TestLoadBadConfigs(t *testing.T) {
+	ch := &ConfigHandler{
+		Config: &Config{},
+	}
+
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{
+			input: "testdata/config-bad-auth-module.yaml",
+			want:  "Error parsing config file \"testdata/config-bad-auth-module.yaml\": yaml: unmarshal errors:\n  line 3: field pretendauth not found in type config.AuthModule",
+		},
+		{
+			input: "testdata/config-bad-extra-field.yaml",
+			want:  "Error parsing config file \"testdata/config-bad-extra-field.yaml\": yaml: unmarshal errors:\n  line 8: field doesNotExist not found in type config.AuthModule",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.input, func(t *testing.T) {
+			got := ch.ReloadConfig(test.input, nil)
+			if got == nil || got.Error() != test.want {
+				t.Fatalf("ReloadConfig(%q) = %v, want %s", test.input, got, test.want)
+			}
+		})
+	}
+}