How to mark an angle using the angles library of pgf 3

Question

I currently adapting tkz-euclide with pgf 3 and I do not see how to mark an angle with tikz without tkz-euclide

with tkz-euclide :

\documentclass[a4paper]{article}
\usepackage{tkz-euclide}
\usetkzobj{all} 
\begin{document}    
\begin{tikzpicture} 
   \tkzInit 
   \tkzDefPoint(2,1){S} 
   \tkzDefPoint(7,3){T}
   \tkzDefPointBy[rotation=center S angle 60](T)\tkzGetPoint{P}    
   \tkzLabelPoint[above right](P){$P$}
   \tkzLabelPoint[below right](S){$S$}
   \tkzLabelPoint[below right](T){$T$}
   \tkzDrawPoints(S,T,P)
   \tkzDrawLines(T,S S,P)
   \tkzMarkAngle[size = 2,mark = ||,arc=l,double,color = blue](T,S,P)%
   \tkzLabelAngle[pos = 1.5](T,S,P){$60^{\circ}$}%
\end{tikzpicture}
\end{document}

with only tikz :

    pic["$\alpha$", draw=blue, -,double, angle eccentricity=1.5, 
    angle radius=2cm] {angle = T--S--P};

but now how to put the mark ? I try with decoratebut without success !