Sim7600 SSL support v.0.12.0

[floBik]

Co-authored-by: @Matt-Stedman

The following PR is an evolution of PR #767 and should resolve issue #786 . A few things have been done:

• Bump to v0.12.0 of TinyGSM
• Refactoring of certificate handling
• updated readme
• some bug fixes

Feel free to test this and give some feedback if something should be changed.

[apanagar]

First off, thanks for this work. This PR looks like exactly what I was looking for. I'm currently trying to run this code on the sim7600 but it seems like the String class in framework-arduino-sam doesn't have an isEmpty method: https://github.com/arduino/ArduinoCore-sam/blob/master/cores/arduino/WString.h

Currently getting the following error trace:

Processing due (platform: atmelsam; board: due; framework: arduino)
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Verbose mode can be enabled via `-v, --verbose` option
CONFIGURATION: https://docs.platformio.org/page/boards/atmelsam/due.html
PLATFORM: Atmel SAM (8.3.0) > Arduino Due (Programming Port)
HARDWARE: AT91SAM3X8E 84MHz, 96KB RAM, 512KB Flash
DEBUG: Current (atmel-ice) External (atmel-ice, blackmagic, jlink, stlink)
PACKAGES: 
 - framework-arduino-sam @ 1.6.12 
 - framework-cmsis @ 1.40500.0 (4.5.0) 
 - framework-cmsis-atmel @ 1.2.2 
 - toolchain-gccarmnoneeabi @ 1.70201.0 (7.2.1)
LDF: Library Dependency Finder -> https://bit.ly/configure-pio-ldf
LDF Modes: Finder ~ chain, Compatibility ~ soft
Found 6 compatible libraries
Scanning dependencies...
Dependency Graph
|-- StreamDebugger @ 1.0.1
|-- TinyGSM @ 0.12.0
Building in release mode
Compiling .pio/build/due/src/main.cpp.o
Compiling .pio/build/due/FrameworkArduinoVariant/variant.cpp.o
Compiling .pio/build/due/FrameworkArduino/IPAddress.cpp.o
Compiling .pio/build/due/FrameworkArduino/Print.cpp.o
Compiling .pio/build/due/FrameworkArduino/Reset.cpp.o
Compiling .pio/build/due/FrameworkArduino/RingBuffer.cpp.o
Compiling .pio/build/due/FrameworkArduino/Stream.cpp.o
Compiling .pio/build/due/FrameworkArduino/UARTClass.cpp.o
Compiling .pio/build/due/FrameworkArduino/USARTClass.cpp.o
Compiling .pio/build/due/FrameworkArduino/USB/CDC.cpp.o
In file included from lib/TinyGSM/src/TinyGsmClient.h:55:0,
                 from src/main.cpp:100:
lib/TinyGSM/src/TinyGsmClientSIM7600.h: In member function 'virtual int TinyGsmSim7600::GsmClientSecureSim7600::connect(const char*, uint16_t, int)':
lib/TinyGSM/src/TinyGsmClientSIM7600.h:362:51: error: 'class String' has no member named 'isEmpty'
       if (certValidation && at->certificates[mux].isEmpty()) {return -1;}
                                                   ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h: In member function 'virtual void TinyGsmSim7600::GsmClientSecureSim7600::stop(uint32_t)':
lib/TinyGSM/src/TinyGsmClientSIM7600.h:372:30: error: 'class String' has no member named 'isEmpty'
       if (!certificates[mux].isEmpty()) {
                              ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:376:36: error: 'class String' has no member named 'isEmpty'
       if (!clientCertificates[mux].isEmpty()) {
                                    ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:380:35: error: 'class String' has no member named 'isEmpty'
       if (!clientPrivateKeys[mux].isEmpty()) {
                                   ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h: In member function 'bool TinyGsmSim7600::modemConnect(const char*, uint16_t, uint8_t, SSLVersion, int)':
lib/TinyGSM/src/TinyGsmClientSIM7600.h:913:30: error: 'class String' has no member named 'isEmpty'
       if (!certificates[mux].isEmpty()) {
                              ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:919:36: error: 'class String' has no member named 'isEmpty'
       if (!clientCertificates[mux].isEmpty()) {
                                    ^~~~~~~
In file included from lib/TinyGSM/src/TinyGsmClient.h:55:0,
                 from src/main.cpp:100:
lib/TinyGSM/src/TinyGsmClientSIM7600.h:924:35: error: 'class String' has no member named 'isEmpty'
       if (!clientPrivateKeys[mux].isEmpty()) {
                                   ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:929:30: error: 'class String' has no member named 'isEmpty'
       if (!certificates[mux].isEmpty() &&!clientCertificates[mux].isEmpty() && !clientPrivateKeys[mux].isEmpty()) {
                              ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:929:67: error: 'class String' has no member named 'isEmpty'
       if (!certificates[mux].isEmpty() &&!clientCertificates[mux].isEmpty() && !clientPrivateKeys[mux].isEmpty()) {
                                                                   ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:929:104: error: 'class String' has no member named 'isEmpty'
       if (!certificates[mux].isEmpty() &&!clientCertificates[mux].isEmpty() && !clientPrivateKeys[mux].isEmpty()) {
                                                                                                        ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:931:36: error: 'class String' has no member named 'isEmpty'
       } else if (certificates[mux].isEmpty() && !clientCertificates[mux].isEmpty() && !clientPrivateKeys[mux].isEmpty()) {
                                    ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:931:74: error: 'class String' has no member named 'isEmpty'
       } else if (certificates[mux].isEmpty() && !clientCertificates[mux].isEmpty() && !clientPrivateKeys[mux].isEmpty()) {
                                                                          ^~~~~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:931:111: error: 'class String' has no member named 'isEmpty'
       } else if (certificates[mux].isEmpty() && !clientCertificates[mux].isEmpty() && !clientPrivateKeys[mux].isEmpty()) {
                                                                                                               ^~~~~~~
src/main.cpp: In function 'void loop()':
src/main.cpp:239:15: error: no matching function for call to 'TinyGsmSim7600::GsmClientSecureSim7600::stop()'
   client.stop();
               ^
In file included from lib/TinyGSM/src/TinyGsmClient.h:55:0,
                 from src/main.cpp:100:
lib/TinyGSM/src/TinyGsmClientSIM7600.h:368:11: note: candidate: virtual void TinyGsmSim7600::GsmClientSecureSim7600::stop(uint32_t)
      void stop(uint32_t maxWaitMs) override {
           ^~~~
lib/TinyGSM/src/TinyGsmClientSIM7600.h:368:11: note:   candidate expects 1 argument, 0 provided
*** [.pio/build/due/src/main.cpp.o] Error 1
===================================================================== [FAILED] Took 1.04 seconds =====================================================================

https://registry.platformio.org/tools/platformio/framework-arduino-sam
Using the Arduino Due specifically because the sim7600 tx/rx are 3.3v and the Due natively supports 3.3v.

Thanks again