Get's the TenantId (and other info) from the domain name

Get-TenantIdByDomainName.ps1

$domain = "contoso.com"

Invoke-WebRequest -Uri "https://login.windows.net/$domain/v2.0/.well-known/openid-configuration" | ConvertFrom-Json

<#
token_endpoint                        : https://login.windows.net/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/oauth2/v2.0/token
token_endpoint_auth_methods_supported : {client_secret_post, private_key_jwt, client_secret_basic}
jwks_uri                              : https://login.windows.net/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/discovery/v2.0/keys
response_modes_supported              : {query, fragment, form_post}
subject_types_supported               : {pairwise}
id_token_signing_alg_values_supported : {RS256}
response_types_supported              : {code, id_token, code id_token, id_token token}
scopes_supported                      : {openid, profile, email, offline_access}
issuer                                : https://login.microsoftonline.com/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/v2.0
request_uri_parameter_supported       : False
userinfo_endpoint                     : https://graph.microsoft.com/oidc/userinfo
authorization_endpoint                : https://login.windows.net/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/oauth2/v2.0/authori
                                        ze
device_authorization_endpoint         : https://login.windows.net/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/oauth2/v2.0/devicec
                                        ode
http_logout_supported                 : True
frontchannel_logout_supported         : True
end_session_endpoint                  : https://login.windows.net/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/oauth2/v2.0/logout
claims_supported                      : {sub, iss, cloud_instance_name, cloud_instance_host_name...}
kerberos_endpoint                     : https://login.windows.net/1316cd1f-b0c7-4253-a7f3-ccc9041aaag9/kerberos
tenant_region_scope                   : NA
cloud_instance_name                   : microsoftonline.com
cloud_graph_host_name                 : graph.windows.net
msgraph_host                          : graph.microsoft.com
rbac_url                              : https://pas.windows.net

#>