fix: authentication should be array, not struct

[zhongwencool]

Try to fix: #8784

• Ensure authentication type is an array, not struct.

[coveralls]

Pull Request Test Coverage Report for Build 3049800820

• 9 of 13 (69.23%) changed or added relevant lines in 3 files are covered.
• 32 unchanged lines in 16 files lost coverage.
• Overall coverage decreased (-0.02%) to 77.372%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/emqx_authn/src/emqx_authn.erl	0	1	0.0%
apps/emqx_authn/src/emqx_authn_app.erl	8	11	72.73%

Files with Coverage Reduction	New Missed Lines	%
apps/emqx_authn/src/emqx_authn_api.erl	1	85.23%
apps/emqx_conf/src/emqx_conf_schema.erl	1	92.31%
apps/emqx_gateway/src/emqx_gateway_schema.erl	1	90.0%
apps/emqx_machine/src/emqx_machine.erl	1	79.31%
apps/emqx/src/emqx_broker.erl	1	83.52%
apps/emqx/src/emqx_channel.erl	1	86.36%
apps/emqx/src/emqx_config_handler.erl	1	96.34%
apps/emqx/src/emqx_flapping.erl	1	85.11%
apps/emqx/src/emqx_message.erl	1	94.12%
apps/emqx/src/emqx_router_utils.erl	1	60.47%

Totals
Change from base Build 3049512272:	-0.02%
Covered Lines:	20632
Relevant Lines:	26666

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💛 - Coveralls

[zmstone]

could you post the new error message (in case e.g. mechanism is missing as reported in the issue)?

[zhongwencool]

could you post the new error message (in case e.g. mechanism is missing as reported in the issue)?

2022-09-15T18:08:07.652351+08:00 [error] line: 71, mfa: emqx_authn_app:initialize/0, msg: failed_to_initialize_authentication, reason: {invalid_config,"mechanism_field_required"}
2022-09-15T18:08:07.652758+08:00 [error] crasher: initial call: application_master:init/4, pid: <0.2396.0>, registered_name: [], exit: {{{failed_to_initialize_authentication,{invalid_config,"mechanism_field_required"}},{emqx_authn_app,start,[normal,[]]}},[{application_master,init,4,[{file,"application_master.erl"},{line,142}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,226}]}]}, ancestors: [<0.2395.0>], message_queue_len: 1, messages: [{'EXIT',<0.2397.0>,normal}], links: [<0.2395.0>,<0.1673.0>], dictionary: [], trap_exit: true, status: running, heap_size: 376, stack_size: 29, reductions: 167; neighbours:
2022-09-15T18:08:07.656996+08:00 [critical] app: emqx_authn, line: 88, mfa: emqx_machine_boot:start_one_app/1, msg: failed_to_start_app, reason: {emqx_authn,{{failed_to_initialize_authentication,{invalid_config,"mechanism_field_required"}},{emqx_authn_app,start,[normal,[]]}}}
2022-09-15T18:08:07.657447+08:00 [error] Supervisor: {local,emqx_machine_sup}. Context: start_error. Reason: {'EXIT',{{failed_to_start_app,emqx_authn,{emqx_authn,{{failed_to_initialize_authentication,{invalid_config,"mechanism_field_required"}},{emqx_authn_app,start,[normal,[]]}}}},[{emqx_machine_boot,start_one_app,1,[{file,"emqx_machine_boot.erl"},{line,89}]},{lists,foreach,2,[{file,"lists.erl"},{line,1342}]},{emqx_machine_boot,post_boot,0,[{file,"emqx_machine_boot.erl"},{line,38}]},{supervisor,do_start_child_i,3,[{file,"supervisor.erl"},{line,414}]},{supervisor,do_start_child,2,[{file,"supervisor.erl"},{line,400}]},{supervisor,'-start_children/2-fun-0-',3,[{file,"supervisor.erl"},{line,384}]},{supervisor,children_map,4,[{file,"supervisor.erl"},{line,1250}]},{supervisor,init_children,2,[{file,"supervisor.erl"},{line,350}]},{gen_server,init_it,2,[{file,"gen_server.erl"},{line,423}]},{gen_server,init_it,6,[{file,"gen_server.erl"},{line,390}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,226}]}]}}. Offender: id=emqx_machine_boot,pid=undefined.
2022-09-15T18:08:07.657931+08:00 [error] crasher: initial call: application_master:init/4, pid: <0.1913.0>, registered_name: [], exit: {{{shutdown,{failed_to_start_child,emqx_machine_boot,{'EXIT',{{failed_to_start_app,emqx_authn,{emqx_authn,{{failed_to_initialize_authentication,{invalid_config,"mechanism_field_required"}},{emqx_authn_app,start,[normal,[]]}}}},[{emqx_machine_boot,start_one_app,1,[{file,"emqx_machine_boot.erl"},{line,89}]},{lists,foreach,2,[{file,"lists.erl"},{line,1342}]},{emqx_machine_boot,post_boot,0,[{file,"emqx_machine_boot.erl"},{line,38}]},{supervisor,do_start_child_i,3,[{file,"supervisor.erl"},{line,414}]},{supervisor,do_start_child,2,[{file,"supervisor.erl"},{line,400}]},{supervisor,'-start_children/2-fun-0-',3,[{file,"supervisor.erl"},{line,384}]},{supervisor,children_map,4,[{file,"supervisor.erl"},{line,1250}]},{supervisor,init_children,2,[{file,"supervisor.erl"},{line,350}]},{gen_server,init_it,2,[{file,"gen_server.erl"},{line,423}]},{gen_server,init_it,6,[{file,"gen_server.erl"},{line,390}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,226}]}]}}}},{emqx_machine_app,start,[normal,[]]}},[{application_master,init,4,[{file,"application_master.erl"},{line,142}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,226}]}]}, ancestors: [<0.1912.0>], message_queue_len: 1, messages: [{'EXIT',<0.1914.0>,normal}], links: [<0.1912.0>,<0.1673.0>], dictionary: [], trap_exit: true, status: running, heap_size: 1598, stack_size: 29, reductions: 239; neighbours:

[thalesmg]

Is this feasible to test? If so, it might be worth adding a test case for that.