In the template that ShareLaTeX offers the bibliography section is done by hand in the end. I think this isn't really necessary here. Unless you are not bound to it you could use the canonical \bibliographystyle-\bibliography pair and define a custom toc macro which temporarilly disables clearpage:
\newcommand\TOCwithBibliography[2][plain]{%
\begingroup
\let\clearpage\relax
\tableofcontents
\vspace{2em}
\bibliographystyle{#1}
\bibliography{#2}
\endgroup
\clearpage
}
Then use \TOCwithBibliography[<bib style>]{<bib file>} at the point your contents+bibliography page should be printed. Of course you could also hard-code the bib style and the bib file information like
...
\vspace{2em}
\bibliographystyle{plain}% or whatever style
\bibliography{testbib}% name of your .bib file
\endgroup
...
But I don't think this is necessarily better.
Complete Example
using llncs.cls v2.6
% arara: pdflatex
% arara: bibtex
% arara: pdflatex
% arara: pdflatex
\RequirePackage{filecontents}
\begin{filecontents}{testbib.bib}
@article{test123,
author = {Rufus Dufus},
title = {Some article},
journal = {Some journal},
year = {2017}
}
\end{filecontents}
\documentclass{llncs}
\usepackage{makeidx}
\usepackage{natbib}
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage[T1]{fontenc}
\usepackage{float}
%\usepackage[nottoc,notlof,notlot]{tocbibind}
\newcommand\TOCwithBibliography[2][plain]{%
\begingroup
\let\clearpage\relax
\tableofcontents
\vspace{2em}
\bibliographystyle{#1}
\bibliography{#2}
\endgroup
\clearpage
}
\begin{document}
\frontmatter
\TOCwithBibliography{testbib}
\nocite{*}
\pagestyle{headings}
\chapter{foo}
\chapter{bar}
\chapter{baz}
\end{document}
Output

Addendum
Note that in the complete example I commented out the tocbibind package as it is quite strange to force the bibliography into the TOC when it is on the same page.
Moreover the alternative approach I showed above may come in handy if you want to redefine \tableofcontents (if you want to keep the markup untouched):
\let\oldtoc\tableofcontents
\renewcommand\tableofcontents{%
\begingroup
\let\clearpage\relax
\oldtoc
\vspace{2em}
\bibliographystyle{plain}
\bibliography{yourbibfile}
\endgroup
\clearpage
}
Lastly you might want to be aware of this question which deals with forcing the TOC onto one page.
biblatex. – moewe Jan 21 '17 at 16:11