Replacing variables in files with value from another file

Question

I have an input file which contains variable and their values.

$ cat input.txt
var1=SomethingNew
var2=SecondPrhase
classpath=/this/is/some/path

I have another directory in which there are multiple files across many sub-directories with these variables. I want to replace all these variables in all files with values from above "input.txt" file. Thanks in advance.