Like literally every programming language should have an implementation of HMAC-SHA1 around and lacking that, at least a SHA1 implementation. It's pretty trivial to build HMAC-<HASHFUNCTION> if you have <HASHFUNCTION> around. A working python implementation is literally 12 lines long.
Now if you don't have a SHA1 implementation in your programming language, that's a different problem.
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Like literally every programming language should have an implementation of HMAC-SHA1 around and lacking that, at least a SHA1 implementation. It's pretty trivial to build HMAC-<HASHFUNCTION> if you have <HASHFUNCTION> around. A working python implementation is literally 12 lines long.
Now if you don't have a SHA1 implementation in your programming language, that's a different problem.