Expose OAuth2 Endpoint Parameters to cli (#5427)

The user may which to control the endpoint parameters for instance to
set the audience when requesting an access token. Exposing the
parameters as a map allows for additional use cases without requiring
modification.

app/vmagent/remotewrite/client.go

@@ -58,6 +58,7 @@ var (
 	oauth2ClientID         = flagutil.NewArrayString("remoteWrite.oauth2.clientID", "Optional OAuth2 clientID to use for the corresponding -remoteWrite.url")
 	oauth2ClientSecret     = flagutil.NewArrayString("remoteWrite.oauth2.clientSecret", "Optional OAuth2 clientSecret to use for the corresponding -remoteWrite.url")
 	oauth2ClientSecretFile = flagutil.NewArrayString("remoteWrite.oauth2.clientSecretFile", "Optional OAuth2 clientSecretFile to use for the corresponding -remoteWrite.url")
+	oauth2EndpointParams   = flagutil.NewMapString("remoteWrite.oauth2.endpointParams", "Optional OAuth2 endpoint parameters to use for the corresponding -remoteWrite.url")
 	oauth2TokenURL         = flagutil.NewArrayString("remoteWrite.oauth2.tokenUrl", "Optional OAuth2 tokenURL to use for the corresponding -remoteWrite.url")
 	oauth2Scopes           = flagutil.NewArrayString("remoteWrite.oauth2.scopes", "Optional OAuth2 scopes to use for the corresponding -remoteWrite.url. Scopes must be delimited by ';'")
 
@@ -238,6 +239,7 @@ func getAuthConfig(argIdx int) (*promauth.Config, error) {
 			ClientID:         oauth2ClientID.GetOptionalArg(argIdx),
 			ClientSecret:     promauth.NewSecret(clientSecret),
 			ClientSecretFile: clientSecretFile,
+			EndpointParams:   *oauth2EndpointParams,
 			TokenURL:         oauth2TokenURL.GetOptionalArg(argIdx),
 			Scopes:           strings.Split(oauth2Scopes.GetOptionalArg(argIdx), ";"),
 		}

docs/CHANGELOG.md

@@ -28,6 +28,7 @@ The sandbox cluster installation is running under the constant load generated by
 
 ## tip
 
+* FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): expose ability to set additional endpoint parameters when requesting an OAuth2 token via a the flag `remoteWrite.oauth2.endpointParams`. See [these docs](https://docs.victoriametrics.com/vmagent.html#advanced-usage).
 * FEATURE: [vmauth](https://docs.victoriametrics.com/vmauth.html): add ability to proxy incoming requests to different backends based on the requested host via `src_hosts` option at `url_map`. See [these docs](https://docs.victoriametrics.com/vmauth.html#generic-http-proxy-for-different-backends).
 * FEATURE: [vmctl](https://docs.victoriametrics.com/vmctl.html): rename cmd-line flag `vm-native-disable-retries` to `vm-native-disable-per-metric-migration` to better reflect its meaning.
 * FEATURE: all VictoriaMetrics components: add ability to specify arbitrary HTTP headers to send with every request to `-pushmetrics.url`. See [`push metrics` docs](https://docs.victoriametrics.com/#push-metrics).

docs/vmagent.md

@@ -1921,6 +1921,9 @@ See the docs at https://docs.victoriametrics.com/vmagent.html .
   -remoteWrite.oauth2.clientSecretFile array
      Optional OAuth2 clientSecretFile to use for the corresponding -remoteWrite.url
      Supports an array of values separated by comma or specified via multiple flags.
+  -remoteWrite.oauth2.endpointParams array
+     Optional OAuth2 endpointParams to use for the corresponding -remoteWrite.url. Keys and values must be seperated by ':'.
+     Supports and array of key:value pairs seperated by comma or specified via multiple flags.
   -remoteWrite.oauth2.scopes array
      Optional OAuth2 scopes to use for the corresponding -remoteWrite.url. Scopes must be delimited by ';'
      Supports an array of values separated by comma or specified via multiple flags.

lib/flagutil/map.go

@@ -0,0 +1,49 @@
+package flagutil
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+)
+
+type MapString map[string]string
+
+// String returns a string representation of the map.
+func (m *MapString) String() string {
+	if m == nil {
+		return ""
+	}
+	return fmt.Sprintf("%v", *m)
+}
+
+// Set parses the given value into a map.
+func (m *MapString) Set(value string) error {
+	if *m == nil {
+		*m = make(map[string]string)
+	}
+	for _, pair := range parseArrayValues(value) {
+		key, value, err := parseMapValue(pair)
+		if err != nil {
+			return err
+		}
+		(*m)[key] = value
+	}
+	return nil
+}
+
+func parseMapValue(s string) (string, string, error) {
+	kv := strings.SplitN(s, ":", 2)
+	if len(kv) != 2 {
+		return "", "", fmt.Errorf("invalid map value '%s' values must be 'key:value'", s)
+	}
+
+	return kv[0], kv[1], nil
+}
+
+// NewMapString returns a new MapString with the given name and description.
+func NewMapString(name, description string) *MapString {
+	description += fmt.Sprintf("\nSupports multiple flags with the following syntax: -%s=key:value", name)
+	var m MapString
+	flag.Var(&m, name, description)
+	return &m
+}