app/vmauth: simplify configuration for src_query_args

Use the shorter form:

src_query_args:
- arg1=value1
- arg2=value2

instead of

src_query_args:
- name: arg1
  value: value2
- name: arg2
  value: value2

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5878

app/vmauth/auth_config.go

@@ -163,13 +163,36 @@ type URLMap struct {
 
 // Regex represents a regex
 type Regex struct {
+	re *regexp.Regexp
+
 	sOriginal string
-	re        *regexp.Regexp
 }
 
+// QueryArg represents HTTP query arg
 type QueryArg struct {
 	Name  string `yaml:"name"`
 	Value string `yaml:"value,omitempty"`
+
+	sOriginal string
+}
+
+// UnmarshalYAML unmarshals up from yaml.
+func (qa *QueryArg) UnmarshalYAML(f func(interface{}) error) error {
+	if err := f(&qa.sOriginal); err != nil {
+		return err
+	}
+
+	n := strings.IndexByte(qa.sOriginal, '=')
+	if n >= 0 {
+		qa.Name = qa.sOriginal[:n]
+		qa.Value = qa.sOriginal[n+1:]
+	}
+	return nil
+}
+
+// MarshalYAML marshals up to yaml.
+func (qa *QueryArg) MarshalYAML() (interface{}, error) {
+	return qa.sOriginal, nil
 }
 
 // URLPrefix represents passed `url_prefix`

app/vmauth/auth_config_test.go

@@ -218,15 +218,6 @@ users:
   - src_query_args: abc
     url_prefix: http://foobar
 `)
-	f(`
-users:
-- username: a
-  url_map:
-  - src_query_args:
-    - name: foo
-      incorrect_value: bar
-    url_prefix: http://foobar
-`)
 
 	// Invalid headers in url_map (missing ':')
 	f(`
@@ -350,8 +341,7 @@ users:
   - src_paths: ["/api/v1/write"]
     src_hosts: ["foo\\.bar", "baz:1234"]
     src_query_args:
-    - name: foo
-      value: bar
+    - 'foo=bar'
     url_prefix: ["http://vminsert1/insert/0/prometheus","http://vminsert2/insert/0/prometheus"]
     headers:
     - "foo: bar"

docs/vmauth.md

@@ -125,12 +125,10 @@ while routing requests with `db=bar` query arg to `http://app2-backend`:
 unauthorized_user:
   url_map:
   - src_query_args:
-    - name: db
-      value: foo
+    - "db=foo"
     url_prefix: "http://app1-backend/"
   - src_query_args:
-    - name: db
-      value: bar
+    - "db=bar"
     url_prefix: "http://app2-backend/"
 ```