Chapter 26 — Identity and access management: architecture alternatives | Engineering Identity and access management

Open, free learning for anyone who wants to protect people and technology. No account is required to read this text or its worked answers.

Lesson map

Lesson 26 published. Map, example, EX076.

flowchart TD
  N0["Learning outcomes"]
  N1["26.1 Alternatives"]
  N2["26.2 Criteria"]
  N3["26.3 Evaluation"]
  N4["26.4 Justification"]
  N5["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4 --> N5
  N5 --> EX["Worked example"]
  EX --> Q["Exercise EX076"]

Logical drawing

flowchart LR
  N0["Learning outcomes"]
  N1["26.1 Alternatives"]
  N2["26.2 Criteria"]
  N3["26.3 Evaluation"]
  N4["26.4 Justification"]
  N5["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> Q["EX076"]

[Learning outcomes]
    |
    v
[26.1 Alternatives]
    |
    v
[26.2 Criteria]
    |
    v
[26.3 Evaluation]
    |
    v
[26.4 Justification]
    |
    v
[Synthesis]
    |
    v
[Worked example] --> [Exercise EX076]

Learning outcomes

You will (1) compare identity architecture alternatives; (2) agree criteria and weights; (3) justify the choice.

26.1 Alternatives

Sana compares three architectures. Option A extends the on-premises directory with federation services for applications. Option B moves staff identity to a cloud identity provider, synchronised from HR, with the on-premises directory retained for laptops and legacy systems. Option C, the do-minimum baseline, keeps local accounts but adds multi-factor authentication to the most sensitive applications and a manual monthly leaver check. Including the do-minimum option gives a fair baseline: every more ambitious option must show enough extra benefit to justify its cost and disruption.

26.2 Criteria

Criteria are agreed with the council before scoring: security benefit, support for phishing-resistant authentication, ability to meet the leaver requirement, cost over five years, operational effort for a three-person team, disruption during migration and fit with existing skills. Weights reflect council priorities, with security benefit and leaver capability weighted highest. Each criterion has a three-level scale with written descriptions of low, medium and high, so scores are consistent and can be challenged cell by cell rather than as a whole.

26.3 Evaluation

Each option is scored with evidence: vendor documentation, a small proof of concept in the test tenant, interviews with the identity team and cost estimates from procurement. Option B scores highest on security and leaver capability and medium on cost. Option A scores well on fit with skills but poorly on operational effort, because the team would maintain more infrastructure. Option C is cheapest but fails the leaver requirement entirely. Sana checks sensitivity: the ranking holds unless cost is weighted far above the council's stated priorities.

26.4 Justification

Sana recommends Option B. The justification explains why it best meets the agreed criteria, acknowledges its weaknesses, such as dependence on a cloud provider and the need for strong internet connectivity, and names the evidence that would change the decision, such as a large rise in subscription prices. Writing plainly lets directors understand and approve it, and future engineers can see whether the reasoning still holds if conditions change, rather than inheriting a decision whose basis is lost. Directors approve the recommendation in writing.

Worked example

Weighted scores rank Option B first, Option A second and Option C last; the ranking survives all weight changes within the council's stated priorities.

Synthetic case. Options, scores and costs are synthetic.

Errors and limits

Comparing a preferred design only against an obviously weak alternative makes the evaluation unconvincing.

Exercises

EX076 — Do-minimum purpose. Why include a do-minimum option?
Show marking criteria
Rubric: 3 = gives a fair baseline others must beat;; 2 = baseline;; 1 = cheapest;; 0 = none.
EX077 — Option C failure. Which requirement does Option C fail?
Show marking criteria
Rubric: 3 = leaver requirement;; 2 = leaver;; 1 = cost;; 0 = none.
EX078 — Decision change evidence. What evidence would change Sana's recommendation?
Show marking criteria
Rubric: 3 = e.g. large subscription price rise;; 2 = price;; 1 = vague;; 0 = none.

Synthesis

Realistic alternatives, agreed criteria, evidence-based scoring and a plain justification produce a defensible architecture choice.

Continue studying — chapter 26 of 50

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