Added get_url to handle authentication

[cezmunsta]

Fixes #680

[shlomi-noach]

Thank you for this!

May I ask for the following changes:

• Extract "curl" outside the function. so that we do:

leader_check=$(curl $(get_curl_auth_params) -m 1 -s -o /dev/null -w "%{http_code}" "${api}/leader-check")

• Only compute the function once, and not per invocation?

[shlomi-noach]

Also, can you please take into account the change in #675?

[cezmunsta]

# ./orchestrator-client -b orchestrator:xxx -c all-instances
10.0.0.20:3306

# ORCHESTRATOR_AUTH_USER=orchestrator ORCHESTRATOR_AUTH_PASSWORD=xxx ./orchestrator-client -c all-instances
10.0.0.2:3306

# ./orchestrator-client -c all-instances                                                                                                              
parse error: Invalid numeric literal at line 1, column 4
^C^

# edit /etc/profile.d/orchestrator-client.sh

# cut -f1 -d= /etc/profile.d/orchestrator-client.sh
ORCHESTRATOR_API

# ./orchestrator-client -c all-instances
10.0.0.2:3306

[cezmunsta]

# ./orchestrator-client -c all-instances
orchestrator-client[26762]: Cannot access orchestrator at http://localhost:3000/api.  Check ORCHESTRATOR_API is configured correctly and orchestrator is running

The value of curl_auth_params is tested against 401 Unauthorized and fails before attempting to execute curl ... instead of erroring on jq

[cezmunsta]

@shlomi-noach OK now?

[shlomi-noach]

@cezmunsta this will unfortunately fail when orchestrator_api contains multiple entries, as per https://github.com/github/orchestrator/pull/681/files#diff-79f20b792813786c70a731862c24143eL157

[shlomi-noach]

As @cezmunsta clarified elsewhere, the check will not fail when orchestrator_api contains multiple entries.