autoconf linking with shared object

[Matt Kowalczyk]

One of my source files uses the library:

#include <openssl/md5.h>

This forces me to add /usr/lib/libcrypto.so to the gcc command when I link the 
object to produce an executable for instance.  My gcc command looks something 
like below:

gcc --pedantic -Wall -std=c99 -O2 -g -O2 /usr/lib/libcrypto.so  -o main  Main.o 
my_md5.o

I was studying autoconf today and was wondering how I can assert that the user 
compiling does in fact have the libcrypto.so shared object.

e.g. ./configure would check to make sure libcrypto.so is available... at least 
it's functionality--the function MD5_Init is defined for example.

Is this possible?

As programs grow in complexity and require many of these shared objects, what is 
the best way to assure portability?  Do I include the code for libcrypto.c for 
the user to compile if they don't have libcrypto.so?  Or do I provide the user 
with an unfriendly error message from the compiler.

Also, the location of my libcrypto.so object may differ from other peoples.  How 
do I deal with that?

Thanks,
Matt