First initial tests

.clangd

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+CompileFlags:
+    Add:
+        - "-I../nginx/src/core"
+        - "-I../nginx/objs"
+        - "-I../nginx/src/os/unix"
+        - "-I/opt/homebrew/Cellar/pcre2/10.47/include"
+        - "-I/opt/homebrew/Cellar/openssl@3/3.6.0/include"

Makefile

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+ngx-http-pow: ngx-http-pow.c
+	cc -o ngx-http-pow \
+		-I../nginx/src/core \
+		-I../nginx/objs \
+		-I../nginx/src/os/unix \
+		-I/opt/homebrew/Cellar/pcre2/10.47/include \
+		-I/opt/homebrew/Cellar/openssl@3/3.6.0/include \
+		-L../nginx/objs/src/core \
+		-L/opt/homebrew/Cellar/pcre2/10.47/lib \
+		-L/opt/homebrew/Cellar/openssl@3/3.6.0/lib \
+		-lssl \
+		-lcrypto \
+		ngx-http-pow.c
+
+.PHONY: run
+run: ngx-http-pow
+	./ngx-http-pow

ngx-http-pow.c

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+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_string.h>
+
+#include <openssl/hmac.h>
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+
+#define NGX_HTTP_POW_RAND_LEN 64
+
+typedef struct {
+    ngx_uint_t  version;
+    ngx_uint_t  created;
+    ngx_uint_t  validity;
+    ngx_uint_t  hardness;
+    u_char      random[NGX_HTTP_POW_RAND_LEN];
+    u_char      hmac[EVP_MAX_MD_SIZE];
+} ngx_http_pow_challenge;
+
+/*
+const u_char *ngx_http_pow_challenge_to_string(ngx_http_pow_challenge *c,
+        ngx_str_t *str)
+{
+    u_char  random_hex[NGX_HTTP_POW_RAND_LEN * 2 + 1];
+    u_char  hmac_hex[EVP_MAX_MD_SIZE * 2 + 1];
+
+    ngx_hex_dump(random_hex, c->random, NGX_HTTP_POW_RAND_LEN);
+    random_hex[NGX_HTTP_POW_RAND_LEN * 2] = 0;
+    ngx_hex_dump(hmac_hex, c->hmac, EVP_MAX_MD_SIZE);
+    hmac_hex[EVP_MAX_MD_SIZE * 2] = 0;
+
+    char out[1024] = { 0 };
+
+    sprintf(out,
+            "version=%lu, created=%lu, validity=%lu, hardness=%lu, random=%s, hmac=%s",
+            c->version, c->created, c->validity, c->hardness, random_hex,
+            hmac_hex);
+
+    printf("%s\n", out);
+
+    return NULL;
+}
+*/
+
+const bool ngx_http_pow_sign_challenge(ngx_http_pow_challenge *c, ngx_str_t *k)
+{
+    size_t         clen;
+    const EVP_MD  *digest;
+
+    clen = sizeof(ngx_http_pow_challenge) - EVP_MAX_MD_SIZE;
+    digest = EVP_sha256();
+
+    u_char *hmac = HMAC(digest, k->data, k->len, (const unsigned char *) c, 
+            clen, c->hmac, NULL);
+
+    return hmac == c->hmac;
+}
+
+int main(int argc, char** argv)
+{
+    ngx_http_pow_challenge c = {
+        .version = 1,
+        .created = 1234567,
+        .validity = 300,
+        .hardness = 22,
+        .random = { 'a', 'b', 'c' },
+        .hmac = { 0 }
+    };
+
+    ngx_str_t key = ngx_string("asdf");
+    bool success = ngx_http_pow_sign_challenge(&c, &key);
+    printf("Success: %d\n", success);
+    printf("challenge:\n");
+    printf("    version: %lu\n", c.version);
+    printf("    created: %lu\n", c.created);
+    printf("    validity: %lu\n", c.validity);
+    printf("    hardness: %lu\n", c.hardness);
+    printf("    random: %.*s\n", NGX_HTTP_POW_RAND_LEN, (char *) c.random);
+    printf("    random: %.*s\n", EVP_MAX_MD_SIZE, (char *) c.hmac);
+
+    // ngx_http_pow_challenge_to_string(&c, NULL);
+	
+    return 0;
+}