diff --git a/acceptance/auth/oauth/out.requests.txt b/acceptance/auth/oauth/out.requests.txt
index 2234d54b8..25e0fbf3a 100644
--- a/acceptance/auth/oauth/out.requests.txt
+++ b/acceptance/auth/oauth/out.requests.txt
@@ -1,3 +1,3 @@
 {"headers":{"User-Agent":"cli/[DEV_VERSION] databricks-sdk-go/[SDK_VERSION] go/[GO_VERSION] os/[OS]"},"method":"GET","path":"/oidc/.well-known/oauth-authorization-server","body":""}
-{"headers":{"Authorization":"Basic Y2xpZW50X2lkOmNsaWVudF9zZWNyZXQ=","User-Agent":"cli/[DEV_VERSION] databricks-sdk-go/[SDK_VERSION] go/[GO_VERSION] os/[OS]"},"method":"POST","path":"/oidc/v1/token","body":"Z3JhbnRfdHlwZT1jbGllbnRfY3JlZGVudGlhbHMmc2NvcGU9YWxsLWFwaXM="}
+{"headers":{"Authorization":"Basic Y2xpZW50X2lkOmNsaWVudF9zZWNyZXQ=","User-Agent":"cli/[DEV_VERSION] databricks-sdk-go/[SDK_VERSION] go/[GO_VERSION] os/[OS]"},"method":"POST","path":"/oidc/v1/token","body":"grant_type=client_credentials\u0026scope=all-apis"}
 {"headers":{"Authorization":"Bearer oauth-token","User-Agent":"cli/[DEV_VERSION] databricks-sdk-go/[SDK_VERSION] go/[GO_VERSION] os/[OS] cmd/current-user_me cmd-exec-id/[UUID] auth/oauth-m2m"},"method":"GET","path":"/api/2.0/preview/scim/v2/Me","body":""}
diff --git a/libs/testserver/server.go b/libs/testserver/server.go
index 03db53aa3..42fd5fde3 100644
--- a/libs/testserver/server.go
+++ b/libs/testserver/server.go
@@ -68,7 +68,9 @@ func (s *Server) Handle(pattern string, handler HandlerFunc) {
 				// as is, which is what we want because the body is already a JSON.
 				reqBody = json.RawMessage(body)
 			} else {
-				reqBody = body
+				// JSON marshal encodes []byte to base64. Typecase it to string
+				// to avoid this.
+				reqBody = string(body)
 			}
 
 			s.Requests = append(s.Requests, Request{