chore(oauth): Switch from using basic auth to token when calling `int…

…rospect`

# Issue

Basic auth has been deprecated when calling `introspect` and bearer
token auth is now recommended:
https://docs.cloudfoundry.org/api/uaa/version/77.19.0/index.html#introspect-token

src/autoscaler/cf/client.go

@@ -320,7 +320,8 @@ func (c *CtxClient) introspectToken(ctx context.Context, token string) (*Introsp
 	if err != nil {
 		return nil, err
 	}
-	request.SetBasicAuth(c.conf.ClientID, c.conf.Secret)
+
+	c.addAuth(ctx, request)
 	request.Header.Set("Content-Type", "application/x-www-form-urlencoded;charset=utf-8")
 
 	resp, err := c.Client.Do(request)
@@ -345,3 +346,13 @@ func (c *CtxClient) introspectToken(ctx context.Context, token string) (*Introsp
 
 	return introspectionResponse, nil
 }
+
+func (c *CtxClient) addAuth(ctx context.Context, req *http.Request) error {
+	tokens, err := c.GetTokens(ctx)
+	if err != nil {
+		return fmt.Errorf("get token failed: %w", err)
+	}
+
+	req.Header.Set("Authorization", TokenTypeBearer+" "+tokens.AccessToken)
+	return nil
+}