Did anyone get hardware flow control of ESP8266 to work on NUCLEO-F091RC to work?

My setup is like the following:
Mbed ESP8266
PA_2 PIN11/UART0_RXD
PA_3 PIN12/UART0_TXD
PA_0 IO15/PIN6/UART0_RTS
PA_1 IO13/PIN5/UART0_CTS

"esp8266.debug": true,
"esp8266.tx": "PA_2",
"esp8266.rx": "PA_3",
"esp8266.rts": "PA_0",
"esp8266.cts": "PA_1",

I always get AT timeout when trying to connect to WiFi. If RTS and CTS pins are removed from target override in mbed_app.json, the setup will work just fine.

What I am doing wrong here? Similar setup seems to work on F429Z board.