Lower tiers of SaaS products are more-or-less strictly designed for:
- individuals or very small businesses where everyone is friends
- who don't have exacting requirements/audit/traceability/reporting concerns
- who are willing to accept some pain/inconvenience if they use it outside of its design parameters
Credential-sharing services in the age of SSO are a dirty workaround designed to circumvent SaaS product segmentation (which would otherwise cause established companies to effectively subsidise tiny startups). I'm all for hacker philosophy, and perhaps this applies less to your situation than it does to the OP, but I do think the idea of credential-sharing is a horrible kludge that has only risen to prominence because of the specific issue that I mentioned, and which only leads to more problems with things like non-repudiation.
- Sign up for free or with a credit card, but you'll run into problems (or at the very least friction/complications) if you end up trying to use if you something serious
- Speak to a salesperson and have your CFO sign the company up for a long-term strategic partnership.
The examples that you gave are less clear-cut though. Trello Business is $12.50 per month, and supports Google Apps SSO. Trello Enterprise supports general SSO, and costs $20.83 per month. Slack pricing is $6.67/mo for Standard, and $12.50/mo for Plus with SSO. None of these are costs that should really make or break the profitability of a company; considering that the business is using them to generate revenue or to reduce its expenses, how do they compare to other things like property/facilities expenses and employee salaries/benefits?
Many of those cool things take night or weekend to set up and that’s kind of fun to do. Regular patching and potential troubleshooting is the less fun part you get to do when adopting a new app.
For everything else, you can put your services behind i.e. traefik and write a middleware, or use something like caddy which has a plugin for sso.
Otherwise, thanks to many providers like Okta and others, SSO should really be a feature provided to smaller tiers nowadays.
We're a small business (2 founders, 3 contractors), and we'd love to use SSO for everything. But we're too small to afford enterprise tiers for things like Slack, Gitlab, etc.
Hopefully this trickles down eventually.
Update: I'd like to add that we provide a SaaS product as well, and have considered adding SSO to the enterprise tier but after much research we can't really find a good reason to restrict it (apart from "everyone else is doing it", and potential manual config).
But both SAML and OpenID connect have discovery protocols. Again, this CAN technically be self-configured by the right customer. But then, maybe the solution is to have a one-time config fee, rather than require a certain tier.