No authorization for assignment: User &1 to profile &2 in system &3

What causes this issue?

The authorizations required depend on the setting of the switch
CHECK_S_USER_SAS in table PRGN_CUST:
If CHECK_S_USER_SAS is not maintained or not equal to YES
Authorizations are required for the following three authorization
objects :
S_USER_GRP with ACTVT = 22 and CLASS = &v1&<(>,<)>
S_USER_PRO with ACTVT = 22 and PROFILE = &v2&<(>,<)>
S_USER_SYS with ACTVT = 78 and SUBSYSTEM = &v3&.
CHECK_S_USER_SAS = YES
In this case, an authorization for object S_USER_SAS with the following
values is required:
ACTVT = 22, CLASS = &v1&, PROFILE = &v2&, SUBSYSTEM = &v3&, any value
for ACT_GROUP.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Caution:
If the profile assignment is performed by Remote Function Call (RFC),
the authorization checks relate to the user specified in the definition
of the RFC connection (transaction SM59) in the target system.

System Response

The profile assignment was not performed.

How to fix this error?

Identify the missing authorizations and have your user administrator
assign these to you.

Error message extract from SAP system. Copyright SAP SE.