Why local variable located always before other variable in stack

I debug the next code:

/* filename: sample.c */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int check_authentication(char *password) {
    int auth_flag = 0;
    char password_buffer[16];
    strcpy(password_buffer, password);
    return auth_flag;
}

int main(int argc, char *argv[]) {
    if(argc < 2) {
        printf("Usage: %s <string>\n", argv[0]);
        exit(0);
    }
    if(check_authentication(argv[1])) {
        puts("Yay");
    }
}

an examination of memory shows that auth_flag is located before password_buffer in memory even if I swap them in definition step:

int check_authentication(char *password) {
    char password_buffer[16];
    int auth_flag = 0;
    strcpy(password_buffer, password);
    return auth_flag;
}

Let's gdb -q ./sample.out:

break 11
run AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
(gdb) i r rsp rbp
rsp            0x7fffffffd980   0x7fffffffd980
rbp            0x7fffffffd9c0   0x7fffffffd9c0
(gdb) x/20xw $rsp
0x7fffffffd980: 0x00000009  0x00000000  0xffffdefe  0x00007fff
0x7fffffffd990: 0xffffd9f8  0x00007fff  0x00f0b5ff  0x00000000
0x7fffffffd9a0: 0x41414141  0x41414141  0x41414141  0x41414141
0x7fffffffd9b0: 0x41414141  0x41414141  0x41414141  0x41414141
0x7fffffffd9c0: 0x41414141  0x41414141  0x41414141  0x41414141
(gdb) x/x &auth_flag 
0x7fffffffd99c: 0x00000000
(gdb) x/x &password_buffer 
0x7fffffffd9a0: 0x41414141

So, why is that? The stack grows upward toward lower memory addresses and auth_flag first defined in check_authentication's stack frame must locate before password_buffer, meaning have higher address.