I fear someone is going to tell me that this was already built-in, but since I couldn’t find it, here is PBKDF2 for Postgres:

```
create or replace function PBKDF2 (salt bytea, pw text, count integer, desired_length integer, algorithm text)
returns bytea
immutable
language plpgsql
as $$
declare
hash_length integer;
block_count integer;
output bytea;
the_last bytea;
xorsum bytea;
i_as_int32 bytea;
i integer;
j integer;
k integer;
begin
algorithm := lower(algorithm);
case algorithm
when 'md5' then
hash_length := 16;
when 'sha1' then
hash_length = 20;
when 'sha256' then
hash_length = 32;
when 'sha512' then
hash_length = 64;
else
raise exception 'Unknown algorithm "%"', algorithm;
end case;
block_count := ceil(desired_length::real / hash_length::real);
for i in 1 .. block_count loop
i_as_int32 := E'\\\\000\\\\000\\\\000'::bytea || chr(i)::bytea;
i_as_int32 := substring(i_as_int32, length(i_as_int32) - 3);
the_last := salt::bytea || i_as_int32;
xorsum := HMAC(the_last, pw::bytea, algorithm);
the_last := xorsum;
for j in 2 .. count loop
the_last := HMAC(the_last, pw::bytea, algorithm);
--
-- xor the two
--
for k in 1 .. length(xorsum) loop
xorsum := set_byte(xorsum, k - 1, get_byte(xorsum, k - 1) # get_byte(the_last, k - 1));
end loop;
end loop;
if output is null then
output := xorsum;
else
output := output || xorsum;
end if;
end loop;
return substring(output from 1 for desired_length);
end $$;
select encode(PBKDF2('123456', 'password', 1000, 16, 'sha256'), 'hex');
```