HTTP SD: Validate HTTP config

Fixes #12762

Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>

config/config_test.go

@@ -1857,6 +1857,10 @@ var expectedErrors = []struct {
 		filename: "http_url_no_host.bad.yml",
 		errMsg:   "host is missing in URL",
 	},
+	{
+		filename: "http_token_file.bad.yml",
+		errMsg:   "at most one of bearer_token & bearer_token_file must be configured",
+	},
 	{
 		filename: "http_url_bad_scheme.bad.yml",
 		errMsg:   "URL scheme must be 'http' or 'https'",

config/testdata/http_token_file.bad.yml

@@ -0,0 +1,6 @@
+scrape_configs:
+  - job_name: foo
+    http_sd_configs:
+      - url: http://foo
+        bearer_token: foo
+        bearer_token_file: foo

discovery/http/http.go

@@ -99,7 +99,7 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if parsedURL.Host == "" {
 		return fmt.Errorf("host is missing in URL")
 	}
-	return nil
+	return c.HTTPClientConfig.Validate()
 }
 
 const httpSDURLLabel = model.MetaLabelPrefix + "url"