I had a problem installing Composer with MAMP for Windows 10. My php.ini file was not in the same directory as php.exe . I assume that the composer does not know how to search elsewhere.
Try making a copy of your php.ini from C:\UwAmp\bin\apache\php.ini by pasting it into C:\UwAmp\bin\php\php-5.4.31 , and then try running Composer setup again. Make sure extension=php_openssl.dll not commented out with ; .
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