Read service definitions from standalone .yml files

Introduces the *services_dir* configuration parameter.

README.md

@@ -47,6 +47,11 @@ The YAML file should contain a dictionary with the following attributes:
 
 * `services` is a dictionary describing all known services and their
   authentication parameters. See the *Service definition* section below
+* `services_dir` (optional) points at a directory containing service
+  configuration. Besides describing services in the main configuration
+  file (using the `services` attribute), it is possible to define
+  additional services in YAML-encoded files (having a *.yml*
+  extension), which is more automation-friendly.
 * `rate_limits` defines the global rate limiters and blacklists. See
   the *Rate limiting* section below.
 * `enabled_backends` is the list of user backends that should be

server/authserver.go

@@ -210,6 +210,9 @@ type Config struct {
 	// Service-specific configuration.
 	Services map[string]*ServiceConfig `yaml:"services"`
 
+	// If set, load more service definitions from *.yml files in this directory.
+	ServicesDir string `yaml:"services_dir"`
+
 	// Named rate limiter configurations.
 	RateLimiters map[string]*authRatelimiterConfig `yaml:"rate_limits"`
 
@@ -288,6 +291,20 @@ func (c *Config) compile() error {
 	return nil
 }
 
+// Load a standalone service configuration: a YAML-encoded file that
+// may contain one or more ServiceConfig definitions.
+func loadStandaloneServiceConfig(path string) (map[string]*ServiceConfig, error) {
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	var out map[string]*ServiceConfig
+	if err = yaml.Unmarshal(data, &out); err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 // LoadConfig loads the configuration from a YAML-encoded file.
 func LoadConfig(path string) (*Config, error) {
 	data, err := ioutil.ReadFile(path)
@@ -295,9 +312,28 @@ func LoadConfig(path string) (*Config, error) {
 		return nil, err
 	}
 	config := Config{path: path}
-	if err := yaml.Unmarshal(data, &config); err != nil {
+	if err = yaml.Unmarshal(data, &config); err != nil {
 		return nil, err
 	}
+
+	// Load service definitions from a directory if necessary, and
+	// merge them into config.Services.
+	if config.ServicesDir != "" {
+		files, _ := filepath.Glob(filepath.Join(config.ServicesDir, "*.yml"))
+		for _, f := range files {
+			if strings.HasPrefix(filepath.Base(f), ".") {
+				continue
+			}
+			tmp, err := loadStandaloneServiceConfig(f)
+			if err != nil {
+				return nil, fmt.Errorf("%s: %v", f, err)
+			}
+			for name, svc := range tmp {
+				config.Services[name] = svc
+			}
+		}
+	}
+
 	if err := config.compile(); err != nil {
 		return nil, err
 	}