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diff --git a/modules/ssl/ssl_engine_init.c b/modules/ssl/ssl_engine_init.c
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index 8b6c34f..3587fb5 100644
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--- a/modules/ssl/ssl_engine_init.c
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+++ b/modules/ssl/ssl_engine_init.c
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@@ -1609,6 +1609,10 @@ static apr_status_t ssl_init_proxy_certs(server_rec *s,
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     STACK_OF(X509) *chain;
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     X509_STORE_CTX *sctx;
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     X509_STORE *store = SSL_CTX_get_cert_store(mctx->ssl_ctx);
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+    int addl_chain = 0; /* non-zero if additional chain certs were
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+                         * added to store */
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+
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+    ap_assert(store != NULL); /* safe to assume always non-NULL? */
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 #if OPENSSL_VERSION_NUMBER >= 0x1010100fL
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     /* For OpenSSL >=1.1.1, turn on client cert support which is
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@@ -1653,20 +1657,28 @@ static apr_status_t ssl_init_proxy_certs(server_rec *s,
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         }
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     }
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-    if ((ncerts = sk_X509_INFO_num(sk)) <= 0) {
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-        sk_X509_INFO_free(sk);
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-        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s, APLOGNO(02206)
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-                     "no client certs found for SSL proxy");
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-        return APR_SUCCESS;
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-    }
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-
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     /* Check that all client certs have got certificates and private
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-     * keys. */
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-    for (n = 0; n < ncerts; n++) {
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+     * keys.  Note the number of certs in the stack may decrease
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+     * during the loop. */
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+    for (n = 0; n < sk_X509_INFO_num(sk); n++) {
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         X509_INFO *inf = sk_X509_INFO_value(sk, n);
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+        int has_privkey = inf->x_pkey && inf->x_pkey->dec_pkey;
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+
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+        /* For a lone certificate in the file, trust it as a
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+         * CA/intermediate certificate. */
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+        if (inf->x509 && !has_privkey && !inf->enc_data) {
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+            ssl_log_xerror(SSLLOG_MARK, APLOG_DEBUG, 0, ptemp, s, inf->x509,
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+                           APLOGNO(10261) "Trusting non-leaf certificate");
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+            X509_STORE_add_cert(store, inf->x509); /* increments inf->x509 */
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+            /* Delete from the stack and iterate again. */
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+            X509_INFO_free(inf);
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+            sk_X509_INFO_delete(sk, n);
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+            n--;
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+            addl_chain = 1;
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+            continue;
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+        }
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-        if (!inf->x509 || !inf->x_pkey || !inf->x_pkey->dec_pkey ||
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-            inf->enc_data) {
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+        if (!has_privkey || inf->enc_data) {
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             sk_X509_INFO_free(sk);
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             ap_log_error(APLOG_MARK, APLOG_STARTUP, 0, s, APLOGNO(02252)
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                          "incomplete client cert configured for SSL proxy "
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@@ -1683,13 +1695,21 @@ static apr_status_t ssl_init_proxy_certs(server_rec *s,
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         }
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     }
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+    if ((ncerts = sk_X509_INFO_num(sk)) <= 0) {
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+        sk_X509_INFO_free(sk);
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+        ap_log_error(APLOG_MARK, APLOG_WARNING, 0, s, APLOGNO(02206)
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+                     "no client certs found for SSL proxy");
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+        return APR_SUCCESS;
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+    }
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+
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     ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(02207)
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                  "loaded %d client certs for SSL proxy",
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                  ncerts);
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     pkp->certs = sk;
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-
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-    if (!pkp->ca_cert_file || !store) {
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+    /* If any chain certs are configured, build the ->ca_certs chains
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+     * corresponding to the loaded keypairs. */
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+    if (!pkp->ca_cert_file && !addl_chain) {
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         return APR_SUCCESS;
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     }
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diff --git a/modules/ssl/ssl_private.h b/modules/ssl/ssl_private.h
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index 2a08d1c..8055200 100644
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--- a/modules/ssl/ssl_private.h
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+++ b/modules/ssl/ssl_private.h
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@@ -655,10 +655,13 @@ typedef struct {
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     const char  *cert_file;
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     const char  *cert_path;
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     const char  *ca_cert_file;
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-    STACK_OF(X509_INFO) *certs; /* Contains End Entity certs */
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-    STACK_OF(X509) **ca_certs; /* Contains ONLY chain certs for
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-                                * each item in certs.
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-                                * (ptr to array of ptrs) */
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+    /* certs is a stack of configured cert, key pairs. */
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+    STACK_OF(X509_INFO) *certs;
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+    /* ca_certs contains ONLY chain certs for each item in certs.
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+     * ca_certs[n] is a pointer to the (STACK_OF(X509) *) stack which
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+     * holds the cert chain for the 'n'th cert in the certs stack, or
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+     * NULL if no chain is configured. */
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+    STACK_OF(X509) **ca_certs;
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 } modssl_pk_proxy_t;
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 /** stuff related to authentication that can also be per-dir */