Vertical border on the left on left page and right on right pages with \AddToShipoutPicture

Question

I have the following code that add some vertical border on pages but it's always on the same side (i.e. left side). So, for twoside documents, it won't look fine.

With the lesser changes, how to make it appear on the right on right pages and on the left on left pages?

\documentclass[a4paper,12pt,twoside]{article}
\usepackage[utf8]{inputenc}
\usepackage[british]{babel}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage{eso-pic,picture}
\usepackage{xcolor}
\definecolor{gray4}{rgb}{0.4,0.4,0.4}
\definecolor{gray8}{rgb}{0.8,0.8,0.8}

\makeatletter
\AddToShipoutPicture{%
  \AtPageLowerLeft{%
    \hspace*{0.48cm}\rotatebox{90}{%
      \colorbox{gray8!44}{%
        \begin{minipage}{\paperheight}
          \sffamily
          \vspace*{0.4em}
          \centering
          \hspace*{\stretch{1}}
          \textcolor{gray4}{some vertical text here along the pages}
          \hspace*{\stretch{1}}
          \vspace*{0.4em}
        \end{minipage}%
      }%
    }%
  }%
}%
\makeatother

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}

\newpage{}
\section{Intro}
\newpage{}
\section{Methods}
\newpage{}

\end{document} 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Answer 1

I found a solution but I had an issue (that I can't reproduce with my MWE, so it must be in conflict with some other package) with the footmisc package that I had to place before the new one in the preamble:

\documentclass[a4paper,12pt,twoside]{article}
\usepackage[utf8]{inputenc}
\usepackage[british]{babel}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage{eso-pic,picture}
\usepackage{xcolor}
\definecolor{gray4}{rgb}{0.4,0.4,0.4}
\definecolor{gray8}{rgb}{0.8,0.8,0.8}
\usepackage[bottom]{footmisc}
\usepackage{scrextend} % New package inserted !


\makeatletter
\AddToShipoutPicture{%
 \ifthispageodd{% define by newly inserted package ! It's an if{true}{false} structure.
  \AtPageLowerLeft{%
   \put(\LenToUnit{\dimexpr\paperwidth-1.8cm},0){%
    \hspace*{0.48cm}\rotatebox{90}{%
      \colorbox{gray8!44}{%
        \begin{minipage}{\paperheight}
          \sffamily
          \vspace*{0.4em}
          \centering
          \hspace*{\stretch{1}}
          \footnotesize{\textcolor{gray4}{some vertical text here along the pages}}
          \hspace*{\stretch{1}}
          \vspace*{0.4em}
        \end{minipage}%
      }%
    }% 
   }%
  }%
 }%
 {
  \AtPageLowerLeft{%
    \hspace*{0.48cm}\rotatebox{90}{%
      \colorbox{gray8!44}{%
        \begin{minipage}{\paperheight}
          \sffamily
          \vspace*{0.4em}
          \centering
          \hspace*{\stretch{1}}
           \footnotesize{\textcolor{gray4}{some vertical text here along the pages}}    
          \hspace*{\stretch{1}}
          \vspace*{0.4em}
        \end{minipage}%
      }%
    }%
   }%
 }%

}%
\makeatother

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}

\newpage{}
\section{Intro}
\newpage{}
\section{Methods}
\newpage{}

\end{document} 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%