Making block diagram of an op-amp configuration
On the input side( without the consideration of Cin),

I1(s)=Vin(s)*sC1 ;


On the output side,

       I2(s)=Vout(s) ( sC2 + 1/R) ;
i.e.,  I2(s)=Vout(s) (sRC2 + 1)/R ;


Since, 

I1(s)=I2(s)


So, 

Vout(s)/Vin(s) = sRC1/(1 + sRC2) ;


Comparing with Closed loop transfer function 

Gain= G(s)/(1+G(s)H(s))  ;

G(s) = sRC1 ; H(s)= C2/C1 ;