Adding sections such as Linkedin and Github to a Moderncv footer

Here's one way to do it adding to new fields \github and \linkedin; the information will be automatically added to the footer, with hyperlinks and some logos (for the logos I used the images obtained with the code at the end of this answer):

\documentclass[11pt,a4paper,sans]{moderncv}
\moderncvstyle{casual}
\usepackage[scale=0.75]{geometry}

\makeatletter

\newcommand*{\linkedin}[1]{\def\@linkedin{#1}}
\newcommand*{\github}[1]{\def\@github{#1}}
\newcommand*{\externallink}[2][]{%
  \ifthenelse{\equal{#1}{}}%
    {\href{#2}{#2}}%
    {\href{#2}{#1}}}
\newcommand\githublogo{\raisebox{-1pt}{\includegraphics[height=9pt]{github}}\ }
\newcommand\linkedinlogo{\raisebox{-1pt}{\includegraphics[height=9pt]{linkedin}}\ }

\renewcommand*{\makecvfooter}{%
  \setlength{\footerwidth}{0.8\textwidth}%
  \fancypagestyle{plain}{%
    \fancyfoot[c]{%
      \parbox{\footerwidth}{%
        \centering%
        \color{color2}\addressfont%
        \ifthenelse{\isundefined{\@addressstreet}}{}{\addtofooter[]{\addresssymbol\@addressstreet}%
          \ifthenelse{\equal{\@addresscity}{}}{}{\addtofooter[~--~]{\@addresscity}}\flushfooter\@firstfooterelementtrue\\}% if \addresstreet is defined, \addresscity will always be defined but could be empty
        \ifthenelse{\isundefined{\@addressstreettwo}}{}{\addtofooter[]{\addresssymbol\@addressstreettwo}%
          \ifthenelse{\equal{\@addresscitytwo}{}}{}{\addtofooter[~--~]{\@addresscitytwo}}\flushfooter\@firstfooterelementtrue\\}% if \addresstreet is defined, \addresscity will always be defined but could be empty
        \ifthenelse{\isundefined{\@mobile}}{}{\addtofooter{\mobilesymbol\@mobile}}%
        \ifthenelse{\isundefined{\@phone}}{}{\addtofooter{\phonesymbol\@phone}}%
        \ifthenelse{\isundefined{\@fax}}{}{\addtofooter{\faxsymbol\@fax}}%
        \ifthenelse{\isundefined{\@email}}{}{\addtofooter{\emailsymbol\emaillink{\@email}}}%
        \ifthenelse{\isundefined{\@homepage}}{}{\addtofooter{\homepagesymbol\httplink{\@homepage}}}%
        \ifthenelse{\isundefined{\@extrainfo}}{}{\addtofooter{\@extrainfo}}%
        \ifthenelse{\isundefined{\@linkedin}}{}{\addtofooter{\linkedinlogo\externallink{\@linkedin}}}%
        \ifthenelse{\isundefined{\@github}}{}{\addtofooter{\githublogo\externallink{\@github}}}%
        \flushfooter}}}%

  \pagestyle{plain}}


\moderncvcolor{blue}


\firstname{John}
\familyname{Doe}
\title{Resume title (optional)}
\address{street and number}{postcode city}
\mobile{+1~(234)~567~890}
\phone{+2~(345)~678~901}
\fax{+3~(456)~789~012}
\email{[email protected]}
\homepage{www.johndoe.com}
\extrainfo{additional information}
\linkedin{http://co.linkedin.com/in/johndoe}
\github{http://github.com/jdoe}
\quote{Some quote (optional)}


\begin{document}

\makecvtitle

\end{document}

The resulting footer:

enter image description here

The code used to produce the logos (kindly provided by Paulo Cereda):

\documentclass{article}
\usepackage{tikz}

\newcommand{\github}{%
\begin{tikzpicture}[y=0.80pt, x=0.8pt,yscale=-1, inner sep=0pt, outer sep=0pt,opacity=0.4]
  \begin{scope}[shift={(506.69823,386.92617)}]
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\end{tikzpicture}
}

\newcommand{\linkedin}{%
\begin{tikzpicture}[y=0.80pt, x=0.8pt,yscale=-1, inner sep=0pt, outer sep=0pt,opacity=0.4]
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\begin{document}
\linkedin\github
\end{document}

EDIT This solution was already mentioned by @you in the comments, i just overlooked that.


I'm just going to address the tikz drawings of the linkedin and github logo in the answer of @GonzaloMedina and provide a more simple version.

The fontawesome package provides some nice symbols for linkedin, github and lots of more.

\documentclass{article}
\usepackage{fontspec}
\usepackage{fontawesome}
\begin{document}
test
\faGithub 
\faLinkedin
\end{document}

result


As a general rule, you can add any type of additional information using the \extrainfo command, e.g.

\extrainfo{%
  \httplink{www.linkedin.com/in/johndoe}
  \httplink{www.github.com/johndoe}}

This works whatever the style of your resume or letter. You can obviously add pictures or symbols or before the links.

Finally, in case you are using the casual style, the command to produce the bullets that are used to separate footer items is \footersymbol.