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Saved credentials access

Saved credentials in the flash

AutoConnect stores the credentials of the established WiFi connection in the flash memory of the ESP8266/ESP32 module and equips the class to access the credentials from the sketch. You can read, write, or erase the credentials using this class individually. It's the AutoConnectCredential, which provides the way of access to the credentials stored in flash.1

Credentials storage location

The location where AutoConnect saves credentials depends on the module type and the AutoConnect library version, also arduino-esp32 core version. In either case, the location is flash memory, but EEPROM and Preferences (in the nvs2) are used depending on the library versions.

AutoConnect Arduino core
for ESP8266
Arduino core for ESP32
1.0.2 earlier 1.0.3 later
v0.9.12 earlier EEPROM EEPROM (partition) Not supported
v1.0.0 later Preferences (nvs)

(Can be used EEPROM with turning off AUTOCONNECT_USE_PREFERENCES macro)

Preferences (nvs)

However, sketches do not need to know where to store credentials using the commonly accessible AutoConnectCredential API.

If you are using an Arduino core for ESP32 1.0.2 earlier and need to use credentials in EEPROM for backward compatibility, turns off the AUTOCONNECT_USE_PREFERENCES3 macro definition in AutoConnectCredentials.h file. AutoConnect behaves assuming that credentials are stored in EEPROM if AUTOCONNECT_USE_PREFERENCES is not defined.


Include header

#include <AutoConnectCredential.h>



AutoConnectCredential default constructor. The default offset value is 0. In ESP8266 or ESP32 with arduino core 1.0.2 earlier, if the offset value is 0, the credential area starts from the top of the EEPROM. If you use this area in a user sketch, AutoConnect may overwrite that data.

AutoConnectCredential(uint16_t offset);
offsetSpecies offset from the top of the EEPROM for the credential area together. The offset value is from 0 to the flash sector size. This parameter is ignored for AutoConnect v1.0.0 or later with arduino-esp32 core 1.0.3 or later.

Public member functions


bool backup(Stream& out)

Outputs all credentials currently stored by AutoConnect to the stream.

outOutput destination stream.
Return value
trueAll credentials were successfully output.
falseFailed to output.


bool del(const char* ssid)

Delete a credential the specified SSID.

ssidSSID to be deleted.
Return value
trueSuccessfully deleted.
falseFailed to delete.

Clear saved credentials

There is no particular API for batch clearing of all credential data stored by AutoConnect. It is necessary to prepare a sketch function that combines several AutoConnectCredential APIs to erase all saved credentials. The following function is an implementation example, and you can use it to achieve batch clearing.

void deleteAllCredentials(void) {
  AutoConnectCredential credential;
  station_config_t config;
  uint8_t ent = credential.entries();

  while (ent--) {
    credential.load(0, &config);
    credential.del((const char*)&config.ssid[0]);


uint8_t entries(void)

Returns number of entries as contained credentials.

Return value
Number of entries as contained credentials.


int8_t load(const char* ssid, station_config_t* config)

Load a credential entry and store to config.

ssidSSID to be loaded.
Return value
Save the specified SSID's credential entry to station_config_t pointed to by the parameter as config. -1 is returned if the SSID is not saved.


bool load(int8_t entry, station_config_t* config)

Load a credential entry and store to config.

entrySpecifies the index number based 0 to be loaded.
Return value
Save the specified credential entry to station_config_t pointed to by the parameter as config. -1 is returned if specified number is not saved.


bool restore(Stream& in)

The credentials data saved by the backup function is input from Storm and saved as AutoConnect credentials.

inAn input stream of a file containing credential data saved with the backup function.
Return value
trueCredentials successfully restored.
falseFailed to restore.


bool save(const station_config_t* config)

Save a credential entry.

configstation_config_t to be saved.
Return value
trueSuccessfully saved.
falseFailed to save.

The data structures


The saved credential structure is defined as station_config_t in the AcutoConnectCredential header file.

typedef struct {
  uint8_t ssid[32];
  uint8_t password[64];
  uint8_t bssid[6];
  uint8_t dhcp;   /**< 0:DHCP, 1:Static IP */
  union _config {
    uint32_t  addr[5];
    struct _sta {
      uint32_t ip;
      uint32_t gateway;
      uint32_t netmask;
      uint32_t dns1;
      uint32_t dns2;
    } sta;
  } config;
} station_config_t;

The byte size of station_config_t in program memory and stored credentials is different

There is a gap byte for boundary alignment between the dhcp member and the static IP members of the above station_config_t. Its gap byte will be removed with saved credentials on the flash.

The credential entry

A data structure of the credential saving area in EEPROM as the below. 4

byte offset Length Value
8 1 Number of contained entries (uint8_t)
9 2 Container size, excluding size of AC_CREDT and size of the number of entries(width for uint16_t type).
11 variable SSID terminated by 0x00. Max length is 32 bytes.
variable variable Password plain text terminated by 0x00. Max length is 64 bytes.
variable 6 BSSID
variable 1 Flag for DHCP or Static IP (0:DHCP, 1:Static IP)
The following IP address entries are stored only for static IPs.
variable(1) 4 Station IP address (uint32_t)
variable(5) 4 Gateway address (uint32_t)
variable(9) 4 Netmask (uint32_t)
variable(13) 4 Primary DNS address (uint32_t)
variable(17) 4 Secondary DNS address (uint32_t)
variable variable Contained the next entries. (Continuation SSID+Password+BSSID+DHCP flag+Static IPs(if exists))
variable 1 0x00. End of container.

AutoConnectCredential has changed

It was lost AutoConnectCredential backward compatibility. Credentials saved by AutoConnect v1.0.3 (or earlier) will not work properly with AutoConnect v1.1.0. You need to erase the flash of the ESP module using the esptool before the sketch uploading.

esptool -c esp8266 (or esp32) -p [COM_PORT] erase_flash

  1. An example using AutoConnectCredential is provided as an example of a library sketch to delete saved credentials. 

  2. The namespace for Preferences used by AutoConnect is AC_CREDT

  3. Available only for AutoConnect v1.0.0 and later. 

  4. There may be 0xff as an invalid data in the credential saving area. The 0xff area would be reused.