Server-identity/secret has required "value" attribute, but there is now credential-reference too and there is no way how to update existing resource to use another option.

/core-service=management/security-realm=ManagementRealm/server-identity=secret:write-attribute(name=credential-reference, value={clear-text=pass123})            
{
    "outcome" => "failed",
    "failure-description" => "WFLYCTL0105: credential-reference is invalid in combination with value",
    "rolled-back" => true
}
[standalone@localhost:9990 /] /core-service=management/security-realm=ManagementRealm/server-identity=secret:undefine-attribute(name=value
{
    "outcome" => "failed",
    "failure-description" => "WFLYCTL0172: value is required",
    "rolled-back" => true
}

[domain@localhost:9990 /] /host=master/core-service=management/security-realm=ManagementRealm/server-identity=secret:read-resource-description
{
    "outcome" => "success",
    "result" => {
        "description" => "Configuration of the secret/password-based identity of a server or host controller.",
        "deprecated" => {
            "since" => "1.7.0",
            "reason" => "The security-realm configuration is deprecated and may be removed or moved in future versions."
        },
        "access-constraints" => {"sensitive" => {"security-realm" => {"type" => "core"}}},
        "attributes" => {
            "credential-reference" => {
                "type" => OBJECT,
                "description" => "The reference to credential for the secret / password stored in CredentialStore under defined alias or clear text password.",
                "expressions-allowed" => false,
                "required" => false,
                "nillable" => true,
                "alternatives" => ["value"],
                "access-constraints" => {"sensitive" => {"credential" => {"type" => "core"}}},
                "value-type" => {
                    "store" => {
                        "type" => STRING,
                        "description" => "The name of the credential store holding the alias to credential.",
                        "expressions-allowed" => false,
                        "required" => false,
                        "nillable" => true,
                        "alternatives" => ["clear-text"],
                        "requires" => ["alias"],
                        "min-length" => 1L,
                        "max-length" => 2147483647L
                    },
                    "alias" => {
                        "type" => STRING,
                        "description" => "The alias which denotes stored secret or credential in the store.",
                        "expressions-allowed" => true,
                        "required" => false,
                        "nillable" => true,
                        "requires" => ["store"],
                        "min-length" => 1L,
                        "max-length" => 2147483647L
                    },
                    "type" => {
                        "type" => STRING,
                        "description" => "The type of credential this reference is denoting.",
                        "expressions-allowed" => true,
                        "required" => false,
                        "nillable" => true,
                        "min-length" => 1L,
                        "max-length" => 2147483647L
                    },
                    "clear-text" => {
                        "type" => STRING,
                        "description" => "Secret specified using clear text. Check credential store way of supplying credential/secrets to services.",
                        "expressions-allowed" => true,
                        "required" => false,
                        "nillable" => true,
                        "alternatives" => ["store"],
                        "min-length" => 1L,
                        "max-length" => 2147483647L
                    }
                },
                "access-type" => "read-write",
                "storage" => "configuration",
                "restart-required" => "no-services"
            },
            "value" => {
                "type" => STRING,
                "description" => "The secret / password - Base64 Encoded.",
                "expressions-allowed" => true,
                "required" => true,
                "nillable" => true,
                "alternatives" => ["credential-reference"],
                "min-length" => 1L,
                "max-length" => 2147483647L,
                "access-type" => "read-write",
                "storage" => "configuration",
                "restart-required" => "no-services"
            }
        },
        "operations" => undefined,
        "notifications" => undefined,
        "children" => {}
    }
}